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Mineralogy new

  1. 1. MINERALOGY (GEO 121) Arlene E. Dayao
  2. 2. MINERALOGY    Also referred to as mineral science The study of naturally occurring, crystalline substances – minerals Basic to an understanding of the materials largely responsible for our present technologic culture
  3. 3. MINERAL  A naturally occurring homogeneous solid with a definite (but not necessarily fixed) chemical composition and a highly ordered atomic arrangement. It is usually formed by inorganic processes.  naturally occurring – formed by natural processes and not in the laboratory *diamond vs. synthetic diamond *CaCO3 concentric layers in water mains  homogeneous solid – consists of a single solid substance that can not be physically subdivided into simpler chemical compounds *H2O - ice in glaciers *water *liquid mercury mineraloids
  4. 4.  definite chemical composition – can be expressed by a specific chemical formula *Quartz – SiO2 *Dolomite – CaMg(CO3)2 or Ca(Mg,Fe,Mn)(CO3)2  ordered atomic arrangement – has an internal structural framework of atoms or ions arranged in a regular geometric pattern (crystalline) *glass – natural solid but amorphous - mineraloid  formed by inorganic processes – includes some organicallyformed compounds *CaCO3 (aragonite) of mollusk shells *elemental sulfur – formed by bacterial action *iron oxide – precipitated by iron bacteria *mineral fuels - naturally formed but no definite chemical composition and no ordered atomic arrangement
  5. 5. HISTORY OF MINERALOGY         Recent science but the practice of mineralogical arts is as old as human civilization Cave paintings of early humans – used natural pigments such as red hematite (Fe2O3) and black manganese (Mn) Stone Age – flint tools were prized possessions (paleolithic and neolithic ages) Nile Valley – tomb paintings 5000 yrs. ago show busy artificers weighing malachite and precious metals, smelting mineral ores and making delicate gems of lapis lazuli and emerald Bronze Age – other minerals were sought from which metals could be extracted 384-322 BC Aristotle - theorized that all the known substances were composed of water, air, earth, and fire and wrote “Meteorologica” 372-287 BC Greek Philosopher Theophrastus – 1st written work on minerals “De Mineralibus” Pliny (400 yrs. later) recorded mineralogical thought of his time and wrote “Naturalis Historia”
  6. 6. HISTORY OF MINERALOGY      1556 Georgius Agricola, German physician, Father of Mineralogy, published “De Re Metallica” – signaled the emergence of mineralogy as a science - Detailed account of mining practices of the time and includes the first factual account of minerals 1912 US Pres. Herbert Hoover - translated “De Re Metallica” from Latin to English 1669 Nicholas Steno – important contribution to crystallography through his study of quartz crystals - Noted that despite differences in origin, size or habit, the angles between corresponding faces were constant 1780 Carangeot – invented contact goniometer to measure interfacial crystal angles 1783 Romé de I’Lsle – made angular measurements on crystals and formulated the law of consistency of interfacial angle
  7. 7. HISTORY OF MINERALOGY       1784 René Haüy – showed that crystals were built by stacking together tiny identical building blocks which he called integral molecules 1801 Haüy – developed theory of rational indices for crystal faces 1809 Wollaston – invented the reflecting goniometer that permitted highly accurate measurement of the positions of crystal faces 1779 to 1848 Berzelius – developed the principles of our present chemical classification of minerals 1815 Cordier – initiated the immersion method which developed into an important technique for the study of optical properties of mineral fragments 1828 William Nicol – invented a polarizing device that permitted the systematic study of the behavior of light in crystalline substances
  8. 8. HISTORY OF MINERALOGY     Late 19th century Federov, Schoenflies and Barlow – simultaneously developed theories for the internal symmetry and order within crystals which became the foundations for X-ray crystallography 1912 Max von Laue – demonstrated that crystal could diffract X-rays - Proved that for the first time the regular and ordered arrangement of atoms in crystalline material 1914 W.H. Bragg and W.L. Bragg – earliest crystal structure determinations were published 1960s – advent of electron microprobe used in the study of chemistry of minerals on a microscale
  9. 9. ECONOMIC IMPORTANCE OF MINERALS   Before historic time - minerals have played a major role in man’s way of life and standard of living Present day – we depend on minerals in countless ways:  Construction  Manufacture of TV sets  Cosmetics  Household cleansers and abrasives  Textile manufacture  Medical purposes  Manufacture of appliances and furniture  Currency and dollar reserves (gold)  Paint pigments  Fertilizer and fertilizer carriers  Machineries
  10. 10. NAMING OF MINERALS   MINERAL CLASSIFICATION – based on the presence of major chemical component (anions or anionic complex)  Native elements Phosphates  Sulfides Nitrates  Sulfosalts Borates  Oxides and Hydroxides Sulfates  Halides Tungstates  Carbonates Silicates, etc - Requires chemical analysis and measurement of physical properties such as specific gravity, optical properties and x-ray parameters NAMING OF MINERALS – based on some physical property or chemical aspect, named after a locality, a public figure, a mineralogist or any other subject considered appropriate
  11. 11. NAMING OF MINERALS   Examples of mineral names:  Albite (NaAlSi3O8) from Latin albus (white) in allusion to its color  Rhodonite (MnSiO3) from Greek rhodon ( a rose) in allusion to its characteristically pink color  Chromite (FeCr2O4) due to presence of high amounts of chromium  Magnetite (Fe3O4) due to its magnetic property  Franklinite (ZnFe2O4) after a locality (Franklin, New Jersey) where it occurs as the dominant zinc mineral  Sillimanite (Al2SiO3) after Professor Benjamin Silliman of Yale University (1779-1864) International Mineralogical Association (Commission on New Minerals and New Mineral Names) reviews all new mineral descriptions and appropriateness of names
  12. 12. NAMING OF MINERALS   As of 2004 there are over 4,000 species of minerals recognized by the IMA.  150 can be called "common,“  50 are "occasional,“  the rest are "rare" to "extremely rare.“
  13. 13. PHYSICAL PROPERTIES OF MINERALS
  14. 14. PROPERTIES OF MINERALS  Dependent on:  Chemistry of minerals chemical composition of minerals  Structure of minerals geometrical arrangement of the constituent atoms or ions nature of electrical forces that bind the atoms together
  15. 15. PHYSICAL PROPERTIES OF MINERALS  Macroscopic expression of the mineral’s internal makeup, specifically its crystal structure and chemical composition 1. 2. Crystal shape 1. Crystal form 2. Crystal habit Properties based on interaction with light 1. Diaphaneity 2. Luster 3. Streak 4. Play of colors 5. Chatoyancy and asterism 6. Luminescence 3. 3. 3. Mechanical properties 1. Cleavage 2. Fracture 3. Parting 4. Hardness 5. Tenacity Properties related to mass 1. Density 2. Specific gravity Other diagnostic properties
  16. 16. PHYSICAL PROPERTIES OF MINERALS 6. Other diagnostic properties 1. Magnetism 2. Radioactivity 3. Solubility in acids 4. Sensor properties 5. Electrical properties
  17. 17. CRYSTAL SHAPE a. a. Crystal form – the outward appearance of a mineral in a regular geometric shape - external form is the outward expression of the internal ordered atomic arrangement - examples: garnet – dodecahedron pyrite – cubic Crystal habit – general shape of a mineral which also includes irregularities due to growth
  18. 18. CRYSTAL FORMS  If mineral specimens display well-developed crystal forms, geometric form names are used to describe a mineral’s outward appearance:  Prismatic – a crystal with one dimension much longer than the other two  Rhombohedral – having the external form of a rhombohedron  Cubic – having the external form of a cube  Octahedral – with the external form of an octahedron
  19. 19. CRYSTAL HABIT       Crystal habit - typical appearance (shape and size) of crystals the many terms used by mineralogists to describe crystal habits are useful in communicating what specimens of a particular mineral often look like helps in identification of minerals some habits are distinctive of certain minerals, although most minerals exhibit many differing habits (the development of a particular habit is determined by the details of the conditions during the mineral formation/crystal growth) warning: crystal habit may mislead the inexperienced as a mineral's internal crystal system can be hidden or disguised minerals belonging to the same crystal system do not necessarily exhibit the same habit
  20. 20. CRYSTAL HABITS  Factors that influence the type of Crystal Habits:  a combination of two or more crystal forms  trace impurities present during growth  crystal twinning (occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner)  growth conditions (i.e., heat, pressure, space)
  21. 21. HABITS OF CRYSTALS & CRYSTAL AGGREGATES HABIT DESCRIPTION EXAMPLE Acicular Needle-like, slender and/or tapered, from Greek acicula meaning “root” Rutile in quartz, sillimanite Amygdaloidal Almond-shaped Heulandite Anhedral Poorly formed, external crystal faces not developed Olivine Bladed Individual crystals are flattened, blade-like, slender and elongated Kyanite, stibnite Botryoidal or globular Grape-like, hemispherical masses, from Greek botrys meaning “bunch” Smithsonite,Hemimorphite, prehnite, chalcedony, adamite and variscite Columnar Stout, column-like individuals Calcite Coxcomb Aggregated flaky or tabular crystals closely spaced Barite Dendritic or arborescent Tree-like, branching in one or more direction from central point, from dendrron meaning “tree” Magnesite in opal, manganese oxides
  22. 22. CRYSTAL HABITS HABIT DESCRIPTION EXAMPLE Dodecahedral Dodecahedron, 12-sided Garnet Drusy or encrustation Aggregate of minute crystals coating a surface Uvarovite Enantiomorphic Mirror-image habit and optical characteristics; right- and lefthanded crystals Quartz Equant, stout, stubby or blocky Length, width, and breadth roughly equal Zircon Euhedral Well-formed, external crystal faces developed Spinel Fibrous or columnar Extremely slender prisms that are flexible thread-like grains or fibers Tremolite, chrysotile Filiform or capillary Hair-like or thread-like, extremely fine Natrolite Foliated or micaceous Layered structure, parting into thin sheets easily Mica
  23. 23. CRYSTAL HABITS HABIT DESCRIPTION EXAMPLE Granular Aggregates of anhedral crystals 210 mm. in matrix Scheelite Hemimorphic Doubly terminated crystal with two differently shaped ends Hemimorphite Mamillary Breast-like: surface formed by intersecting partial spherical shapes Malachite Massive or compact Shapeless, no distinctive external crystal shape, very fine grained Serpentine, goethite Nodular or tuberose Deposit of roughly spherical form with irregular protuberances Geodes Octahedral Octahedron, eight-sided (two pyramids base to base) Diamond Plumose Fine, feather-like scales Mottramite Prismatic Elongate, prism-like: crystal faces parallel to c-axis well-developed Tourmaline
  24. 24. CRYSTAL HABITS HABIT DESCRIPTION EXAMPLE Pseudohexagonal hexagonal appearance due to cyclic twinning Aragonite Pseudomorphous Occurring in the shape of another mineral through pseudomorphous replacement Tiger's eye Radiating or divergent Acicular crystals radiating outward from a central point Pyrite suns, wavellite, goethite Reniform or colloform Similar to mamillary: intersecting kidney-shaped masses Hematite Reticulated Acicular crystals forming net-like intergrowths Cerussite Rosette Platy, radiating rose-like aggregate Gypsum Sphenoid Wedge-shaped Sphene Stalactitic Forming as stalactites or stalagmites: cylindrical or coneshaped Rhodochrosite
  25. 25. CRYSTAL HABITS HABIT DESCRIPTION EXAMPLE Stellate Star-like, radiating Pyrophyllite Striated/striations Surface growth lines parallel or perpendicular to a crystallographic axis Chrysoberyl Subhedral External crystal faces only partially developed Tabular Flat, tablet-shaped, prominent pinnacoid Ruby Wheat sheaf Aggregates resembling handreaped wheat sheaves Zeolites Lamellar Made up of layers, like the leaves in a book Graphite, molybdenite Banded Single mineral may show a thin and roughly parallel banding, or 2 or more minerals form a finely banded intergrowth Banded malachite, chert and hematite intergrowth
  26. 26. CRYSTAL HABITS HABIT DESCRIPTION EXAMPLE Concentric Bands or layers are arranged concentrically about one or more centers Agate Geode A rock cavity lined with mineral matter but not completely filled. Maybe banded as in agates, containing a central portion filled with euhedral crystals projecting into an open space Oolitic Made up of oolites, which are small, round or ovate accretionary bodies and resemble the roe of fish Oolitic iron ore Pisolitic Made up of pea-sized grains, similar to oolitic but coarser Bauxite
  27. 27. CRYSTAL HABIT Qualities of Crystal Development:  Euhedral – a mineral that is completely bounded by crystal faces (well-formed); from the Greek eu which means “good” and “hedron” meaning “plane”  Subhedral – a mineral grain that is partly bounded by crystal faces and partly by irregular surfaces; from the Greek sub which means “less than”  Anhedral – a mineral that lacks crystal faces and that may show rounded or irregular surfaces; from the Greek an meaning “without”  The qualities are a reflection of the space that was available to the crystal at the time of its growth 
  28. 28. DIAPHANEITY a measure of the amount of light that can be transmitted by a mineral (light-transmitting qualities)  From the Greek work diaphanes meaning “transparent”  Transparent – transmits light allowing objects to be seen through it (ulexite, gemstones)  Transluscent – capable of transmitting light diffusely but it is not ransparent. It does not show a sharp outline of an object seen through it.  Opaque – impervious to visible ligh, even on thin edges of the mineral
  29. 29. LUSTER   Luster – refers to the general appearance of a mineral surface in reflected light Types of Luster:  Metallic – characterized by a brilliant appearance of a metal ̶ Opaque to light ̶ Has black or very dark streak  Sub-metallic – intermediate between metallic and non metallic. ̶ Similar luster to metal, but are duller and less reflective ̶ Often occurs in near-opaque minerals with very high refractive indices, such as sphalerite, cinnabar and cuprite  Non-metallic – generally light colored and transmits light ̶ colorless to very light colored
  30. 30. LUSTER TYPE OF NONMETALLIC LUSTER DESCRIPTION Vitreous Luster of polished glass. One of the most common luster and occurs in transparent or translucent minerals with relatively low refractive indices (eg. calcite, quartz and fluorite) Resinous Has the appearance of resin, chewing gum or smooth-surfaced plastic (eg. amber – a form of fossilized resin, sphalerite and sulfur) Greasy Resembles fat or grease or with a layer of oil. Often occurs in minerals containing a great abun-dance of microscopic inclusions. Many minerals with a greasy lustre also feel greasy (eg. opal and cordierite)
  31. 31. LUSTER TYPE OF NONMETALLIC LUSTER DESCRIPTION Pearly Iridescent pearl-like luster in minerals consisting of thin transparent co-planar sheets. Light reflecting from these layers give them a luster reminiscent of pearls. Such minerals possess perfect cleavage (muscovite mica and stilbite) Silky Silk-like. Caused by the reflection of light from a fine fibrous parallel aggregate (asbestos, ulexite, satin spar, chrysotile and malachite) Adamantine A hard, brilliant luster. Superlative lustre seen in transparent or translucent having a high refractive index, from Greek adamos meaning “shine” (eg. Cerussite,diamond, garnet and zircon)
  32. 32. LUSTER TYPE OF NONMETALLIC LUSTER DESCRIPTION Dull or earthy Exhibits little to no luster, due to coarse granulations which scatter light in all directions, approximating a Lambertian reflector. A distinction is sometimes drawn between dull minerals and earthy minerals, with the latter being coarser, and having even less lustre (eg. Kaolinite, goethite, limonite) Waxy A luster resembling appearance of wax (eg. jade and chalcedony)
  33. 33. STREAK  Streak – color of a finely powdered mineral ̶ usually constant and thus, useful in mineral identification ̶ determined by rubbing the mineral on a piece of unglazed porcelain or streak plate ̶ if no streak seems to be made, the mineral's streak is said to be white or colorless ̶ streak is particularly important as a diagnostic for opaque and colored materials ̶ less useful for silicate minerals, most of which have a white streak and are too hard to powder easily. The streak plate has a hardness of a bout 7 and thus, it cannot be used with minerals with greater hardness
  34. 34. STREAK  Streak ̶ ̶ ̶ ̶ ̶ ̶ ̶ ̶ Examples: Cinnabar (dark red color) dark red streak Azurite (blue color) blue streak Fluorite (green, purple or yellow color) white streak, Hematite (black color) red streak Galena (black color) gray streak Pyrite (brass or gold yellow) green streak Sphalerite (dark brownish black to honey rown) pale yellow streak
  35. 35. COLOR Color – directly related to the chemistry and structure of mineral. When the chemical element causing the color is essential to a mineral, color can be used as a diagnostic tool because such a mineral has a constant color  Sulfur – yellow  Malachite – green  Turquiose – greenish blue to blue-green  most minerals with a metallic luster vary little in color and the color of freshly broken surface of a metallic mineral is diagnostic  Galena – bright bluish lead gray color becomes dull gray  Bornite – brownish-bronze color when fresh and tarnish to iridescent metallic purples and blues (peacock ore) 
  36. 36. COLOR  Color – results in minerals when certain wavelengths of light are absorbed. Color results from the combination of those wavelengths that reach the eye  When light strikes the surface of a mineral, part of it is reflected and part refracted. If light suffers no absorption, the mineral is colorless Pleochroism – selective absorption of light by minerals resulting in a display of different colors when light is transmitted along different crystallographic directions (eg. Cordierite) 
  37. 37. COLOR, STREAK AND OPTICAL PHENOMENA    Dichroism – selective absorption of light along two crystallographic directions resulting in a display of different colors (eg. tourmaline) Idiochromatic minerals – minerals where color serves as an important means of identification  Malachite – green  Azurite – blue  Rhodonite and rhodochrosite – rose red or rose pink  Chalcopyrite – brass yellow  Niccolite – copper red  Bornite – peacock ore Allochromatic minerals – minerals that produce no characteristic colors and colors vary depending on the presence of impurities like Fe
  38. 38. COLOR, STREAK AND OPTICAL PHENOMENA  Play of Colors  the striking play of colors in minerals that result from the interference of light as the angle of incident light changes either at the surface or in the interior of a mineral  Caused by the diffraction of light from closely spaced features such as packed spheres (opal) or fine lamellae within the mineral (plagioclase), closely spaced fractures, cleavage planes or exsolution lamellae  eg. Precious opal – interference of light reflected from sub-microscopic layers of nearly spherical particles arranged in a regular pattern
  39. 39. COLOR, STREAK AND OPTICAL PHENOMENA  Play of Colors  Opalescence – pearly color produced by scattering of light in common opal due to absence of microscopic layering  Iridescence – caused by light defracted and reflected from closely spaced fractures or cleavage planes in parallel orientation or thin surface films (internal and surface) – bornite, hematite, limonite and sphalerite  Schiller - colorful iridescence that occurs when light is reflected between layers (eg. moonstone and labradorite), also called labradorescence
  40. 40. OTHER OPTICAL PHENOMENA  Chatoyancy  the silky appearance which results from closely packed parallel fibers  a display of luminous bands, which appear to move as the specimen is rotated. Such minerals are composed of parallel fibers (or contain fibrous voids or inclusions), which reflect light into a direction perpendicular to their orientation, thus forming narrow bands of light  Examples: Cat's eye (chrysoberyl) Cymophane Tiger’s eye (qtz w/ amphibole)
  41. 41. OTHER OPTICAL PHENOMENA   Asterism  the display of a star-shaped luminous area  triple chatoyancy  Examples: Some sapphires and rubies Aventurescence  is a reflectance effect like that of glitter  It arises from minute, preferentially oriented mineral platelets within the material. These platelets are so numerous that they also influence the material's body color  Examples: aventurine quartz
  42. 42. LUMINESCENCE   Luminescence – emission of light by a mineral that is not a direct result of incandescence  Occurs in minerals containing foreign ions or “activators”  Usually faint and can be seen only in the dark Types of Luminescence:  Fluorescence – luminescence that occurs during exposure of a mineral to ultraviolet light, x-rays or cathode rays  Produced when the energy of shortwave radiation is absorbed by impurity ions and released as longer wave radiation  Color of emitted light varies considerably with wavelengths or source of ultraviolet light  eg. Fluorite (blue fluorescence due to organic materials or rare earth ions), scheelite (pale blue fluorescence due to Mo replacing W), willemite, calcite, diamond, hyalite, scapolite, eucryptite (salmon pink)  Synthetic phospors : fluorescent lamps, paints, cloth and tapes
  43. 43. LUMINESCENCE  Phosphorescence – luminescence that continues after the exciting rays are cut off  Thermoluminescence – visible light emitted by some minerals when heated to a temperature below that of red heat Best shown by non metallic minerals that contain foreign ions as activators eg. Fluorite, chlorophane calcite, apatite, feldspar  Triboluminescence – luminosity of some minerals after having been crushed, scratched or rubbed Mostly occurs in non metallic minerals that possess good cleavage eg. Fluorite, sphalerite, lepidolite
  44. 44. CLEAVAGE, PARTING AND FRACTURE     Cleavage - tendency of crystalline materials to split along definite crystallographic structural planes (parallel to atomic planes) creating smooth surfaces Parallel to crystal faces Result from:  Weak type of bond  Greater spacing between the planes  Combination of the 2 Cleavage quality  Perfect  Good  Fair  obscure  absent
  45. 45. CLEAVAGE, PARTING AND FRACTURE  Types of Cleavage:  Basal or pinacoidal cleavage - occurs parallel to the base of a crystal, the {0001} crystal plane (eg. mica group, graphite)  Cubic cleavage - occurs on the {001} plane parallel to the faces of a cube. This is the source of the cubic shape seen in crystals (eg. ground table salt, halite and galena)  Octahedral cleavage - occurs on the {111} crystal plane forming octahedra shapes. Common semiconductors. (eg. diamond and fluorite)  Dodecahedral cleavage - occurs on the {011} crystal planes forming dodecahedra.(eg. wulfenite and gypsum)  Rhombohedral cleavage - occurs parallel to the {1011} faces of a rhombohedron. (eg. Calcite and other carbonate minerals)  Prismatic cleavage - parallel to a vertical prism {110}. (eg. cerussite, tremolite and spodumene)
  46. 46. CLEAVAGE, PARTING AND FRACTURE
  47. 47. CLEAVAGE, PARTING AND FRACTURE
  48. 48. CLEAVAGE, PARTING AND FRACTURE
  49. 49. CLEAVAGE, PARTING AND FRACTURE
  50. 50. CLEAVAGE, PARTING AND FRACTURE     Parting – tendency for a mineral to break along planes of structural weakness due to external stress or along twin composition planes Result from:  Pressure  Twinning Parting breaks are very similar in appearance to cleavage Types of Parting:  octahedral parting (eg. Magnetite)  rhombohedral parting (eg. Corundum)  basal parting (eg. Pyroxenes)
  51. 51. CLEAVAGE, PARTING AND FRACTURE  Uses/Importance of Cleavage and Parting:  traditional physical property used in mineral identification both in hand specimen and microscopic examination of rock and mineral studies  technical importance in the electronics industry and in the cutting of gemstones  Precious stones are generally cleaved by impact as in diamond cutting
  52. 52. CLEAVAGE, PARTING AND FRACTURE   Fracture – the way a mineral breaks when it does not yield along cleavage or parting surfaces Types of Fracture:  Conchoidal fracture – smooth, curved fracture resembling the interior surface of a shell  Fibrous or splintery fracture –  Hackly fracture – jagged fractures with sharp edges  Uneven or irregular fracture – fractures producing rough and irregular surfaces
  53. 53. HARDNESS Hardness – or “scratchability” is the resistance that a smooth surface of a mineral offers to scratching  Designated by (H)  Dependent on type of bonding and crystal structure  Determined by observing comparative ease or difficulty with which one mineral is scratched by another mineral or by a file or a knife  Uses a scale of 10 Minerals (Mohs Scale)  Mohs Scale of Hardness – introduced by F. Mohs in 1824  arranged in an order of increasing relative hardness  purely ordinal scale (eg. corundum (9) is twice as hard as topaz (8), but diamond (10) is almost four times as hard as corundum)  Absolute hardness – measured using a sclerometer 
  54. 54. HARDNESS  There is a link between hardness and chemical composition  Most hydrous minerals are relatively soft (H <5)  Halides, carbonates, sulfates and phosphates are relatively soft (H <5.5)  Most sulfides are relatively soft (H <5) with pyrite being and exception (H ~6 to 6.5)  Most anhydrous oxides and silicates are hard (H >5.5)
  55. 55. HARDNESS Mohs Scale of Hardness HARDNESS MINERAL ABSOLUTE HARDNESS HARDNESS MINERAL ABSOLUTE HARDNESS 1 Talc (Mg3Si4O10(O H)2) 1 6 Orthoclase (KAlSi3O8) 72 2 Gypsum (CaSO4·2H2 O) 2 7 Quartz (SiO2) 100 3 Calcite (CaCO3) 9 8 Topaz (Al2SiO4(O H-,F-)2) 200 4 Fluorite (CaF2) 21 9 Corundum (Al2O3) 400 5 Apatite (Ca5(PO4)3(O H-,Cl-,F-) 48 10 Diamond (C) 1500
  56. 56. HARDNESS On the Mohs Scale:  pencil lead - 1  fingernail - 2.5  copper penny - 3.5  knife blade - 5.5  window glass - 5.5  steel file - 6.5  Using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale. 
  57. 57. HARDNESS
  58. 58. HARDNESS Intermediate Hardness Hardness 1 2.5 to 3 Substance or Mineral Talc pure gold, silver, aluminum 3 Calcite, copper penny 4 Fluorite 4 to 4.5 Platinum 4 to 5 Iron Hardness Substance or Mineral 7 Quartz 7 to 7.5 Garnet 7 to 8 8 8.5 9 Hardened steel Topaz Chrysoberyl Corundum 5 Apatite 9 to 9.5 6 Orthoclase <10 Ultrahard fullerite 6 Titanium 10 Diamond 6.5 Iron pyrite >10 Aggregated diamond nanorods, Rhenium diboride 6 to 7 Glass, Vitreous pure silica Carborundum
  59. 59. TENACITY Tenacity- the resistance that a mineral offers to breaking, bending, or tearing “cohesiveness” of a mineral  Types:  Brittleness – ability to break or powder easily (halite)  Malleability – the ability to be hammered out into thin sheets (copper)  Sectility – the ability to be cut into thin shavings with a knife (chalcocite)  Ductility – ability to be drawn into wires (gold)  Flexibility – can be bent but does not resume original shape when pressure is released (chlorite, talc)  Elasticity – can be bent and return to original shape upon release of pressure (mica) 
  60. 60. DENSITY AND SPECIFIC GRAVITY  Density – defined as mass per unit volume ρ m = v  Specific gravity – or “relative density”  Designated by (G)  A number that expresses the ratio between the weight of a substance and the weight of an equal volume of water at 4°C  eg. a mineral with a specific gravity of 2 weighs twice as much as the same volume of water  Useful in fine crystal or gemstones when other test could injure the specimen  Dependent on: kind of atoms of which it is composed (eg. Olivine – solid solution series between fosterite Mg2SiO4 with G 3.3 and fayalite Fe2SiO4 with G 4.4)
  61. 61. SPECIFIC GRAVITY Manner in which the atoms are packed together (eg. Diamond – closely packed →3.5 vs. graphite – C atoms loosely packed →2.23)  Average specific gravity for non metallic minerals → G 2.65 to G 2.75 → this is because the specific gravities of the most common non metallic minerals quartz is 2.65, feldspar is 2.6 to 2.75 and calcite is 2.72  ulexite G 1.96 – light, barite G 4.5 – heavy  Average specific gravity for metallic minerals → G 5.0 → this is because the specific gravities of the most common metallic mineral pyrite is 5.0  Graphite G 2.23 – light, silver G 10.5 - heavy
  62. 62. DETERMINATION OF SPECIFIC GRAVITY For accurate determination of specific gravity, the mineral specimen must be:  homogeneous and pure  compact with no cavities or cracks within which bubbles or films of air could be imprisoned  Modes of Specific Gravity Determination:  Jolly balance  Pycnometer 
  63. 63. DETERMINATION OF SPECIFIC GRAVITY:     Weigh the mineral in air (Wa). Immerse in water and weigh again → (Ww). (under these conditions it weighs less, since in water it is buoyed up by a force equivalent to the weight of the displaced water) (Wa – Ww) is equal to the apparent loss of weight or equals the weight of an equal volume of water Specific Gravity (G) = Wa ----------------- Wa – Ww
  64. 64. DETERMINATION OF SPECIFIC GRAVITY BY JOLLY BALANCE:  Place a fragment on the upper scale pan and record the elongation of the spring. This is proportional to the weight in air Wa  Transfer the fragment into the lower pan and immersed in water Record the elongation of the spring. This is proportional to the weight of the fragment in water Ww  Note: *torsion balance used for obtaining specific gravities of small particles weighing less than 25 mg. *because specific gravity is merely a ratio, it is not necessary to determine the absolute weight of the specimen but mere values proportional to the weights in air and water
  65. 65. DETERMINATION OF SPECIFIC GRAVITY BY PYCNOMETER:       Dry pycnometer bottle is weighed (P). Mineral fragments are then introduced into the bottle and a second weighing (M) is made (M – P) represents the weight of the sample in air The bottle containing the mineral sample is partially filled with distilled water and boiled for a few minutes to drive off any air bubbles After cooling, the pycnometer is further filled with distilled water and weighed (S), care being taken that the water rises to the top of the capillary opening but that no excess water is present The last weighing is made (W) is made after emptying the bottle and refilling with distilled water alone
  66. 66. DETERMINATION OF SPECIFIC GRAVITY BY PYCNOMETER:   In the last step, the pycnometer contains more water than in the previous weighing; the volume of water added is equal to the aggregate volume of the grains comprising the sample The specific gravity is determined: G = (M – P) ------------W + (M – P) - S Where: M – P = weight of sample W = pycnometer + water content S = sample + pycnometer + undisplaced water W + (M – P) – S = weight of water displaced by sample  Method used when a mineral can not be obtained in a homogeneous mass large enough to permit use of the balance method
  67. 67. ELECTRICAL PROPERTIES Conduction of electricity in crystals is related to the type of bonding  Pure metallic bonding – excellent conductors  Partially metallic – semi-conductors (some sulfide minerals)  Ionic or covalent bonding – non conductors  Electrical conductivity for non isometric minerals – vectorial property varying with crystallographic direction (eg. Graphite better conductor at right angles to the caxis than parallel to it) 
  68. 68. ELECTRICAL PROPERTIES  PIEZOELECTRICITY  occurs in crystals with polar axis (polar axis is present in crystals that lack a center of symmetry – 21 of the 32 crystal classes have no center of symmetry)  A flow of electrons toward one end producing negative electrical charge while a positive charge is induced at the opposite end if pressure is exerted at the ends of the polar axis  First detected in quartz in 1881 by Pierre and Jacques Curie  Practical uses: sound waves produce by submarines could be detected by the piezoelectric current generated when they impinge on a submerged quartz
  69. 69. ELECTRICAL PROPERTIES  PIEZOELECTRICITY  Practical uses: Piezoelectric property of quartz was first used in 1921 to control radio frequencies. When subjected to an alternating current, a properly cut slice of quartz is mechanically deformed and vibrates by being flexed first one way and then the other, the thinner the slice, the greater the frequency of vibration. By placing a quartz plate in the electric field generated by a radio circuit, the frequency of transmission or reception is controlled when the frequency of the quartz coincides with the oscillations of the circuit
  70. 70. ELECTRICAL PROPERTIES  PIEZOELECTRICITY  Practical uses: Tiny quartz plate used in digital quartz watches serves the same function as quartz oscillators used to control radio frequencies. It mechanically vibrates at a constant predetermined frequency controlling accurately the radio frequency of the electronic circuit in the watch
  71. 71. ELECTRICAL PROPERTIES  PYROELECTRICITY  Observed in crystals with polar axes (primary pyroelectricity is shown in crystals that belong to 10 crystal classes having a unique axis – eg. tourmaline)  Simultaneous development of positive and negative charges at opposite ends of a polar axis due to temperature changes
  72. 72. MAGNETIC PROPERTIES   MAGNETISM  Being attracted to a magnet  Use to separate minerals by magnetic separator Types: a. Ferromagnetic • Being attracted to a small hand magnet (ie. magnetite Fe3O4 and pyrrhotite Fe-xS a. a. Paramagnetic • Minerals containing iron being attracted in a field of powerful electromagnet Diamagnetic • Minerals repelled in a field of powerful electromagnet
  73. 73. RADIOACTIVITY Minerals containing radioactive elements like uranium and thorium will continually undergo decay reactions in which radioactive isotopes of U and Th for various daughter elements  During decay they release energy in the form of alpha and beta particles and gamma radiation  Examples of radioactive minerals: uraninite, pitchblende, thorianite and autunite 
  74. 74. SOLUBLITY IN ACID  Some minerals undergo visible reaction with dilute hydrochloric acid CaCO3 + 2 H → Ca 2+ + CO2 ( gas ) + H 2O As the calcite dissolves, it releases carbon dioxide gas hat bubbles in the liquid, producing the familiar “fizz”  Calcite, aragonite, witherite, and strontianite as well as Cu-carbonates, show bubbling or effervescence when a drop of dilute HCl is placed on the mineral  Other carbonates like, rhodochrosite, dolomite, magnesite and siderite show effervescence only in hot HCl 
  75. 75. SENSORY PROPERTIES  Odor – sulfur smells like the gas produced by rotten egg, Clay smell earthy  Taste – halite taste salty, sylvite tastes salty and bitter  Feel – greasy feel for molybdenite, graphite and talc
  76. 76. CRYSTAL CHEMISTRY
  77. 77. ATOMS AND IONS- THE BUILDING BLOCKS  Matter is made up of atoms.  The structure of atoms dictate their properties. How atoms combine dictate what we see in the many minerals in nature.  New technologies allow us to peer ever closer at the minute structures of minerals, down to the scale of individual atoms
  78. 78. ATOMS AND IONS – THE BUILDINGBLOCKS  Atom is smallest subdivision of matter that retain the characteristics of the elements. Although one can subdivide atoms into numerous subatomic particles, we will be concerned only with protons, neutrons and electrons.  Protons and neutrons are together in the nucleus of an atom, whereas electrons are in motion in orbits around the central nucleus. Protons carry a positive electrical charge, electrons carry a negative charge, and neutrons carry no charge. Neutrons work to keep nuclei together.  Most atoms are electrically neutral, meaning that they have an equal number of protons and electrons
  79. 79. ATOMS AND IONS – THE BUILDING BLOCKS Very small massive nucleus composed of protons and neutrons surrounded by a much larger region populated by electrons, except in Hydrogen  Not visible to naked eye and even with highest magnification of the electron microscope  Sizes are measured as atomic radius in Å (0.46 to 2.62 Å)  Each electron moves in an orbit around the nucleus and carries negative electricity. Distance from nucleus depends on the energies of the electrons  Electrons and nuclei are both extremely small but the electrons move very rapidly around the nuclei → give large effective diameters (10k-20k times) 
  80. 80. ATOMS AND IONS  A schematic model of a lithium (Li) atom in the ground state. It has 3 protons in the nucleus, and 3 electrons in orbit. (we will get to the number of neutrons)
  81. 81. ELECTRONIC AND NUCLEAR PROPERTIES  Properties of atoms reflect some combination of features related to electrons or to the nucleus.  The electronic properties are those related to how atoms connect to one another: bonding.  . The nuclear properties include features like radioact- ivity
  82. 82. SIZE OF NUCLEI The number of neutrons tends to closely follow the number of protons. Atoms with more of each are bigger and heavier. A uranium atom, with 92 protons and ~146 neutrons is gigantic compared to dinky helium (2 + 2).
  83. 83. THE SPACIOUS ATOM Microcosms of our solar system, atoms are dominantly empty space: electron orbits If an oxygen atom had a total radius of 100 km, the nucleus would be a ~1 m diameter sphere in the middle.
  84. 84. ELECTRONS IN ORBIT In a simplistic model, electrons float around the nucleus in orbits that are sometimes called shells. electron orbits As the number of electrons increases, they start to fill orbits farther out from the nucleus. In most cases, electrons are lost or gained only from the outermost orbits.
  85. 85. CHARGED ATOMS: IONS  Left to their own devices, atoms are electrically neutral. That means that they have an equal number of protons and electrons.  During the course of most natural events, protons are not gained or lost, but electrons may be.  Atoms with more or fewer electrons than protons are electrically charged. They are called ions: an atom that loses electrons takes on a positive charge (cation); an atom that gains electrons takes on a negative charge (anion).
  86. 86. ATOMIC NUMBER  We distinguish one element from another on the basis of the atomic number, which is the number of protons.  So, an atom of any element can have a variable number of electrons and neutrons, but given the number of protons, the fundamental properties of the element are unchanged. This is the basis for Dmitri Mendeleev’s organization of the Periodic Table of the Elements. The table is a way of organizing elements on physical grounds, but also serves to group elements with consistent chemical properties.
  87. 87. THE PERIODIC TABLE  The periodic table is read from top to bottom, left to right, as atomic number increases: 1=H, 2=He, 3=Li, 4=Be, 5=B, 6=C, and so on.
  88. 88. THE PERIODIC TABLE alkali earths Elements in columns (groups) have similar outer-electron configurations, and so tend to behave similarly. transition metals alkalis halogens rare earths noble gases actinides
  89. 89. OXIDATION STATE Most atoms will form the same kinds of ions all the time. For example, all the alkalis form +1 ions, and the halogens form -1 ions. alkalis halogens
  90. 90. OXIDIZED AND REDUCED STATES transition metals The transition metals are more electronically complex. They may form ions of various charges. For example, iron (Fe) is found as +2 and +3 ions. A transition metal cation with a higher charge is more oxidized than one of lower charge. That comes from the fact that materials with high proportions of Fe+3/Fe+2 form in environments where oxygen is abundant. The opposite is also true, and we call Fe+2 reduced iron.
  91. 91. THE PERIODIC TABLE: THE BULK EARTH A small number of elements make up >99% of the solid Earth. O = oxygen Na = sodium Mg = magnesium Al = aluminum Si = silicon S = sulfur Ca = calcium Fe = iron Ni = nickel
  92. 92. THE PERIODIC TABLE: THE CRUST The crust is a little more elementally interesting (again, as a result of differentiation), but it is still mainly made of a small number of elements. C = carbon P = phosphorus K = potassium Ti = titanium Mn = manganese
  93. 93. ATOMIC WEIGHT: IT’S ALL IN THE NUCLEUS Since electrons weigh virtually nothing, the mass of an atom is concentrated in its nucleus. Each atom can be described by its atomic weight (or mass), which is the sum of the protons and neutrons. lithium: atomic number = 3 3 protons 4 neutrons atomic weight = 3 + 4 = 7 BUT... although each element has a defined number of protons, the number of neutrons is not fixed. Atoms with the same atomic number but variable numbers of neutrons are called isotopes.
  94. 94. STABLE AND RADIOACTIVE ISOTOPES Carbon (atomic # 6) has three natural isotopes with atomic weights of 12, 13 and 14. isotope #p #n ======== == C-12 6 6 C-13 6 7 C-14 6 8 C-14 is a radioactive isotope; C-12 and C-13 are stable. Over time the proportion of C-12/C-14 and C-13/C-14 will increase until there is no C-14. (unless some process makes new C-14...)
  95. 95. ATOMS AND IONS       Atomic particles can exist only with certain energy configurations (Max Planck) → basis of Quantum Theory Quantum Theory – energy exists on an atomic scale only as discrete bundles and not as an infinitely divisible spectrum Thus, electrons surrounding the nucleus can occupy only specific energy levels which differ by discrete number of quanta Atomic number – the positive charge is the same as the number of protons, and this number, equal to the number of electrons is called the atomic number Z Characteristic mass or mass number – determined by the sum of protons and neutrons Isotopes – atoms of the same element but with differing numbers of neutrons (eg. O with Z=8 : O16, O17 and O18)
  96. 96. ATOMS AND IONS   Atomic weight – number expressing relative weight of an element in terms of the weight of the element oxygen Characteristics of an element depend on the configuration of the electronic structure of its atoms
  97. 97. RADIOACTIVITY INSIDE YOU Concerned about radioactivity in nature? To keep things in perspective, consider that 0.01% of all potassium is radioactive K-40. Potassium is an essential element in the human body. If your body is about 1% K, this means a 70 kg (150 pound) person contains around 1x1021 atoms (that’s one billion trillion atoms) of radioactive K-40.
  98. 98. BONDING FORCES IN CRYSTALS   Forces that bind atoms or ions of crystalline solids together are electrical in nature Type and intensity of bond are responsible for physical and chemical properties of minerals (hardness, cleavage, fusibility, electrical and thermal conductivity and coefficient of thermal expansion)  The stronger the bond → harder crystal → higher melting point → smaller thermal expansion coeff.  Diamond (C) – hardness due to very strong electrical forces linking carbon atoms  Periclase (MgO) and halite (NaCl) – have similar structural patterns but halite melts at 801 °C while periclase at 2800 °C due to stronger electrical bond requiring larger heat energy to separate atoms
  99. 99. BONDING FORCES IN CRYSTALS  One typical consequence of chemical reactions is the formation of chemical bonds between atoms and complexes. What kind of bonds form is based on the electronic configuration of the atoms involved.  Atoms with near-full (halogens) and near-empty (alkalis/alkali earths) outer electron shells, as well as transition metals, may form ionic bonds.  Covalent bonds are where atoms share outer shell electrons.  The bulk of minerals are dominantly ionically bonded. However, many minerals have bonds with some covalent and some ionic components.
  100. 100. BONDING FORCES IN CRYSTALS  Types of Chemical Bonds:  Ionic bond (moderate hardness and SG, high melting and boiling points, poor conductors of heat and electricity)  Covalent bond – strongest chemical bond (very high melting and boiling points, great stability)  Metallic bond (high plasticity, tenacity, ductility and conductivity, low hardness, low melting and boiling points)  Van der Waals’ bond (weak)
  101. 101. ATOMIC STRUCTURE • Protons and neutrons form the nucleus of an atom – Represents tiny fraction of the volume at the center of an atom, but nearly all of the mass • Electrons orbit the nucleus in discrete shells or energy levels – Shells represent nearly all of the volume of an atom, but only a tiny fraction of the mass – Numbers of electrons and protons are equal in a neutral atom – Ordinary chemical reactions involve only outermost shell (valence) electrons
  102. 102. ELECTRONS ORGANIZE IN ENERGY LEVELS
  103. 103. CHEMICAL BONDING • Chemical bonding is controlled by outermost shell (valence) electrons • Elements will typically be reactive unless their valence shell is full • Atoms or groups of atoms with unequal numbers of protons and electrons, thus having a non-zero charge, are called ions. Positively charged ions are known as cations, and negative charges as anions. • Positive and negative ions are attracted to one another and may stick or chemically bond together
  104. 104. IONIC BONDS Atoms satisfy themselves by the give and take of outer shell electrons. Most minerals are held together by primarily ionic bonds.
  105. 105. COVALENT BONDS: ELECTRON SHARING These carbon atoms are held together by sharing outer-shell electrons.
  106. 106. BONDING FORCES IN CRYSTALS PROPERTY IONIC BOND COVALENT BOND METALLIC BOND VAN DER WAAL’S BOND BOND STRENGTH Strong Very strong Variable strength but generally moderate Weak MECHANICAL Moderate to high hardness depending on interionic distance; brittle Great hardness; brittle Low to moderate hardness; gliding common; high plasticity; sectile; ductile; malleable Crystal soft and somewhat plastic ELECTRICAL Poor conductors in solid state, melts and solutions conduct by ion transport Insulators in solid state Good conductors; conduction by electron transport Insulators in both solid and liquid state THERMAL (melting point, coefficient of thermal expansion) Moderate to high MP depending on interionic distance; low coefficient of thermal expansion High MP, low coefficient of thermal expansion Variable MP and coefficient of thermal expansion Low MP, high coefficient of thermal expansion SOLUBILITY Soluble in polar solvents Very low solubilities Insoluble except in acids or alkalis by chemical reaction Soluble in organic solvents to yield solutions STRUCTURAL Non-directed; gives structure of high coordination and symmetry Highly directional; gives structures of lower coordination and symmetry Non-directed; gives structures of very high coordination and symmetry Non-directed; symmetry low because of shape of molecules EXAMPLES Halite (NaCl) Calcite (CaCO3) Fluorite (CaF2) Diamond (C) Sphalerite (ZnS) O2 molecules Graphite C) Organic molecules Copper (Cu) Silver (Ag) Gold (Au) Most metals Iodine (I2) Organic compounds Most minerals
  107. 107. CHEMICAL REACTIONS: ACHIEVING STABILITY  Chemical reactions take place in order to achieve a more stable state (lower total energy) under given conditions (pressure, temperature).  Unstable reactants react to form stable products  To complicate this, the transition from unstable mineral to stable mineral is not necessarily automatic. Many chemical reactions require great deal of energy to run to completion
  108. 108. STABILITY AND METASTABILITY  Minerals that persist in an environment in which they are not chemically stable are said to be metastable.  Most of the minerals in the rocks at the Earth’s surface are metastable. Given enough energy (or enough time and the p re s s u re right conditions) they will react to form stable minerals. d ia m o n d s t a b le g r a p h ite s ta b le Earth’s surface conditions te m p e ra tu re
  109. 109. CHEMICAL COMPOSITION OF MINERALS    Most minerals have compositions corresponding to chemical compounds. But a few occurs as elements (native) such as native gold, native copper and native sulfur Minerals are seldom chemically pure (except quartz and kyanite), and compositions seldom correspond to an ideal chemical formula → “characteristic chemical composition” Chemical formulas – derived from the determination of the principal chemical constituents of a mineral (eg. CuFeS2) ELEMENT ANALYSIS ( wt. %) ATOMIC WEIGHT ATOMIC PROPORTIONS ATOMIC RATIO RECALCULATED PERCENTAGE Cu 34.89 63.54 0.5491 1 34.62 Fe 30.04 55.85 0.53.78 1 30.43 S 34.51 32.07(2) 1.0768 2 34.94 99.44 183.53 100.00
  110. 110. CHEMICAL COMPOSITION OF THE EARTH’S CRUST  Internal structure of the earth:  Core – 2900 to 6370 km.  Inner core – solid (5115 km.)  Outer Core – liquid (2900 km.)  Mantle  Upper mantle – 400 km.  Transition Zone – 1000 km.  Lower Mantle – 2900 km.  Mohorovicic Discontinuity – boundary between the crust and the upper mantle  Crust - 36 km. thick (under continents), 10-13 km (under oceans)  Upper part – large percentage of sedimentary rocks and unconsolidated materials forming as thin veneer  Lower part – basement of igneous and metamorphic rocks  Upper 10 mi. consist of 95% igneous rocks, 4% shale, 0.75% sandstone and 0.25% limestone
  111. 111. CHEMICAL COMPOSITION OF THE EARTH’S CRUST   Average composition – between basalt and granite Most common elements in the earth’s crust (99%): ELEMENT % WEIGHT % VOLUME O 46.60 93.77 Si 27.72 0.86 Al 8.13 0.47 Fe 5.00 0.43 Mg 2.09 0.29 Ca 3.63 1.03 Na 2.83 1.32 K 2.59 1.83
  112. 112. ROCK-FORMING MINERALS       O constitutes >90% of the volume of the earth’s crust Earth’s crust is a packing of O anion with interstitial metal ions, chiefly Si (O-containing minerals such as silicates, oxide and carbonates most abundant minerals) Rock-forming minerals are members of silicate-oxidecarbonate group Economic minerals (eg. Cu, Pb, Hg,) low abundance → locate areas of high concentrations (ore deposits) to make mining profitable and to produce metals needed for our economy Some elements (eg. Rubidium) are dispersed throughout common minerals and are never concentrated. Rb does not form specific Rb compounds but is housed in K-rich minerals Some elements are highly concentrated in some minerals: Zr in zircon (ZrSiO4), Ti in rutile (TiO2) and ilmenite (FeTiO2)
  113. 113. CHEMICAL COMPOSITION OF THE EARTH  Estimates based on composition of meteorites and the Estimates based on composition of meteorites and the volumes of the crust, mantle and core    Core → iron meteorites (FeNi alloy) Lower mantle → meteorites with 50% metal and 50% silicate Upper mantle and lower crust → stony silicate meteorites (with little metal) ELEMENT % COMPOSITION O 29.53 Si 15.20 Al 1.09 Fe 34.63 Mg 12.70 Ca 1.13 Ni 2.39 Na, K, Cr, Co, Mn, P & Ti 0.1 to 1.0
  114. 114. CRYSTALLOGRAPHY
  115. 115. CRYSTALLOGRAPHY  Crystallography - study of crystalline solids and the laws that govern their growth, external shape and internal structure  CRYSTAL – a homogeneous solid possessing long range, three-dimensional internal order  MINERALS – possess internal ordered arrangement that is characteristic of crystalline solids - bounded by smooth plane surfaces and assume regular geometric forms only when conditions are favorable
  116. 116. CRYSTALLOGRAPHY     Study of structure, symmetry and shape of crystals. This terminology defines the crystal lattice which provides a mineral with its ordered internal structure CRYSTAL: 1. Microcrystalline – fine grained that crystalline nature can only be determined using a microscope 2. Cryptocrystalline – very fine that individual crystallites cannot be resolved with microscope but can be detected by x-ray diffraction CRYSTAL (perfection of development) 1. Euhedral – perfectly developed faces 2. Subhedral – imperfectly developed faces 3. Anhedral - without faces AMORPHOUS – lack ordered internal atomic arrangement (mineraloids)
  117. 117. CRYSTALLIZATION  Crystals form from:  Solutions (evaporation of solvent, lowering temperature or pressure) Salt dissolved in water → evaporation → solution contains more and more Na+ and Cl- per unit volume → remaining water can no longer retain all the salt in solution → salt begins to precipitate Slow evaporation → Na+ and Cl- group together and form one or few large crystals with common orientation Rapid evaporation → many centers of crystallization and form many small randomly oriented crystals  Melts Liquid H2O molecules moving freely in any direction → temperature lowering → molecules become fixed and arrange themselves in definite order → solid crystalline mass (ice)
  118. 118. CRYSTALLIZATION   Melts  Molten magma → ions of many elements in an uncombined state → magma cools → various ions are attracted to one another to form crystal nuclei of the different minerals → crystallization proceeds with addition of more ions to the crystal nuclei forming the mineral grains of the resulting rock Vapors  Formation of snowflakes → vapor is cooled, the dissociated atoms or molecules are brought closer together, eventually locking themselves into crystalline solid
  119. 119. CRYSTAL    A crystal consists of matter that is formed from an ordered arrangement of atoms, molecules, or ions. Because there are repeated units, crystals have recognizable structures. There are seven systems of crystal structures, which are also called lattices or space lattices. A crystal or crystalline solid is a solid material, whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. Crystalline structures occur in all classes of materials, with all types of chemical bonds
  120. 120. CRYSTALLOGRAPHIC AXES     In order to study the forms and define the position of the faces occurring on crystals, straight lines are assumed to pass through the ideal center of each crystal. These lines are called the crystallographic axes. Intersections of crystallographic axes forms an axial cross If the 3 crystal axes are identical (eg. octahedron), each is referred to the same letter a. The extremities of the axes are differentiated by the use of the plus and minus signs If the axes are not alike, the one extending from front to rear is termed the a axis, the one from left to right the b axis and the vertical axis as c. They are always referred to in the following order, a, b, and c Grouping of crystal forms into 7 crystal systems is aided by the crystallographic axes
  121. 121. CRYSTALLOGRAPHIC AXES ISOMETRIC TETRAGONAL ORTHORHOMBIC TRIGONAL MONOCLINIC TRICLINIC HEXAGONAL
  122. 122. CRYSTALLOGRAPHIC AXES   crystallographic axes can be defined for the various crystal systems. Two important points to remember: a. The lengths of the crystallographic axes are controlled by the dimensions of the unit cell upon which the crystal is based. b. The angles between the crystallographic axes are controlled by the shape of the unit cell. the relative lengths of the crystallographic axes control the angular relationships between crystal faces. This is true because crystal faces can only develop along lattice points. The relative lengths of the crystallographic axes are called axial ratios.
  123. 123. ELEMENTS OF CRYSTALLIZATION   Axial ratio Angles showing the inclination of the axes
  124. 124. AXIAL RATIO    Axial ratio is defined as the ratio between the lengths of the axes of crystals. This is normally taken as relative to the length of the b crystallographic axis. Thus, an axial ratio is defined as follows: Axial Ratio = a/b : b/b : c/b where a is the actual length of the a crystallographic axis, b, is the actual length of the b crystallographic axis, and c is the actual length of the c crystallographic Axial ratios of a given substance is constant
  125. 125. AXIAL RATIO      In the cubic system, where the 3 axes are identical, the ratio is a : a : a or 1 : 1 : 1 (this is usually shorted to 1) In tetragonal system the lengths the length of the a and b axes are equal, this reduces to 1 : 1 : c/b (this is usually shorted to 1 : c) In hexagonal crystals where there are three equal length axes (a1, a2, and a3) perpendicular to the c axis this becomes 1 : 1 : 1: c/a (usually shortened to 1 : c) In orthorhombic, monoclinic and triclinic systems, there are 3 axes of unequal lengths a, b and c. This redices to a/b : 1 : c/b (this is usually shortened to a : 1 : c) Modern crystallographers can use x-rays to determine the size of the unit cell and determine the absolute value of the crystallographic axes. For example, quartz has the following unit cell dimensions: a1 = a2 = a3 = 4.913Å and c = 5.405Å where: Å stands for Angstroms = 10-10 m
  126. 126. AXIAL RATIO   Thus the axial ratio for quartz is 1 : 1 : 1 : 5.405/4.913 or 1: 1 : 1 : 1.1001 which simply says that the c axis is 1.1001 times longer than the a axes. Because crystal faces develop along lattice points, the angular relationship between faces must depend on the relative lengths of the axes. Long before x-rays were invented and absolute unit cell dimensions could be obtained, crystallographers were able to determine the axial ratios of minerals by determining the angles between crystal faces. So, for example, in 1896 the axial ratios of orthorhombic sulfur were determined to be nearly exactly the same as those reported above from x-ray measurements.
  127. 127.   PARAMETERS AND PARAMETRAL RATIOS In order to determine the position of a face on a crystal, it must be referred to the crystallographic axes Parametral ratios differ from axial ratios which gives the numerical lengths of the axes in terms of one of them taken as unity
  128. 128. INTERCEPTS OF CRYSTAL FACES (WEISS PARAMETERS)   Crystal faces can be defined by their intercepts on the crystallographic axes. For non-hexagonal crystals, there are three cases: 1. A crystal face intersects only one of the crystallographic axes 2. A crystal face intersects two of the crystallographic axes 3. A crystal face that intersects all 3 axes Two very important points about intercepts of faces:  The intercepts or parameters are relative values, and do not indicate any actual cutting lengths.  Since they are relative, a face can be moved parallel to itself without changing its relative intercepts or parameters
  129. 129. CRYSTAL FACE INTERSECTS ONLY ONE OF THE CRYSTALLOGRAPHIC AXES  As an example the top crystal face shown here intersects the c axis but does not intersect the a or b axes. If we assume that the face intercepts the c axis at a distance of 1 unit length, then the intercepts, sometimes called Weiss Parameters, are: a,  b, 1c
  130. 130. CRYSTAL FACE INTERSECTS TWO OF THE CRYSTALLOGRAPHIC AXES  As an example, the darker crystal face shown here intersects the a and b axes, but not the c axis. Assuming the face intercepts the a and c axes at 1 unit cell length on each, the parameters for this face are: 1 a, 1 b,  c
  131. 131. CRYSTAL FACE THAT INTERSECTS ALL THREE AXES  In this example the darker face is assumed to intersect the a, b, and c crystallographic axes at one unit length on each. Thus, the parameters in this example would be: 1a, 1b, 1c
  132. 132. INTERCEPTS OF CRYSTAL FACES   Because one does usually not know the dimensions of the unit cell, it is difficult to know what number to give the intercept of a face, unless one face is chosen arbitrarily to have intercepts of 1. Thus, the convention is to assign the largest face that intersects all 3 crystallographic axes the parameters - 1a, 1b, 1c. This face is called the unit face. For example, in the orthorhombic crystal shown here, the large dark shaded face is the largest face that cuts all three axes. It is the unit face, and is therefore assigned the parameters 1a, 1b, 1c.
  133. 133. INTERCEPTS OF CRYSTAL FACES   Once the unit face is defined, the intercepts of the smaller face can be determined. These are 2a, 2b, 2/3c. Note that we can divide these parameters by the common factor 2, resulting in 1a,1b,1/3c. Again, this illustrates the point that moving a face parallel to itself does not change the relative intercepts. Since intercepts or parameters are relative, they do not represent the actual cutting lengths on the axes. By specifying the intercepts or parameters of a crystal face, we now have a way to uniquely identify each face of a crystal. But, the notation is cumbersome, so crystallographers have developed another way of identifying or indexing faces. This conventional notation called the Miller Index.
  134. 134. MILLER INDICES    Miller indices are a notation system in crystallography for planes and directions in crystal (Bravais) lattices. Miller Indices are a symbolic vector representation for the orientation of an atomic plane in a crystal lattice and are defined as the reciprocals of the fractional intercepts which the plane makes with the crystallographic axes In particular, a family of lattice planes is determined by three integers a, b, and c, the Miller indices. They are written (abc) and each index denotes an intersection of a plane with a direction (a, b, c) in the basis of the reciprocal lattice vectors. By convention, negative integers are written with a bar, as in 3 for −3. The integers are usually written in lowest terms, i.e. their greatest common divisor should be 1. Miller index 100 represents a plane orthogonal to direction a; index 010 represents a plane orthogonal to direction b, and index 001 represents a plane orthogonal to c.
  135. 135. MILLER INDICES  The method by which indices are determined is best shown by example. Recall, that there are three axes in crystallographic systems. Miller indices are represented by a set of 3 integer numbers
  136. 136. MILLER INDICES  Steps to describe the orientation of a crystal face or a plane of atoms within a crystal lattice: 1. The first thing that must be ascertained are the fractional intercepts that the plane/face makes with the crystallographic axes. In other words, how far along the unit cell lengths does the plane intersect the axis. In the figure on the right, the plane intercepts each axis at exact one unit length.
  137. 137. MILLER INDICES 2. 3. 4. Taking the reciprocal of the fractional intercept of each unit length for each axis. In the figure on the right, the values are all 1/1. Finally the fractions are cleared (i.e., make 1 as the common denominator). These integer numbers are then parenthetically enclosed and designate that specific crystallographic plane within the lattice. Since the unit cell repeats in space, the notation actually represents a family of planes, all with the same orientation. In the figure, the Miller indices for the plane is (111)
  138. 138. MILLER INDICES
  139. 139. MILLER INDICES
  140. 140. INTERNAL ORDER AND CRYSTAL MORPHOLOGY   3-D internal order of a crystal – considered as a repetition of a motif* in such a way that the environment of and around each repeated motif is identical Motifs:  Anionic groups (SiO4)-4  Ions (Ca2+, Mg2+, Fe2+) Ordered arrangement provides more stable and less energetic configuration. An ordered pattern is generated by a motif repeated in a regular sequence of new location Any motion that brings the original motif into coincidence with the same motif elsewhere in the pattern is referred to as an operation. Thus a homogeneous pattern can be generated from a single motif by a set of geometric operations.    molecules (H2O)
  141. 141. INTERNAL ORDER AND CRYSTAL MORPHOLOGY    3-D internal order of a crystal – considered as a repetition of a motif in such a way that the environment of and around each repeated motif* is identical Motifs:  Anionic groups (SiO4)-4  molecules (H2O)  Ions (Ca2+, Mg2+, Fe2+) Symmetry** - describes the repetition of structural features 1. Translational symmetry - describes the periodic repetition of a structural feature across a length or through an area or volume 2. Point symmetry - describes the periodic repetition of a structural feature around a point (reflection, rotation, inversion)
  142. 142. INTERNAL ORDER AND CRYSTAL MORPHOLOGY   Lattice - a network or array composed of single motif which has been translated and repeated at fixed intervals throughout space (imaginary) - directly related to the idea of translational symmetry - eg. square → planar square lattice Unit cell of a lattice - the smallest unit which can be repeated in three dimensions in order to construct the lattice - consists of a specific group of atoms which are bonded to one another in a set geometrical arrangement. - this unit and its constituent atoms are then repeated over and over in order to construct the crystal lattice. The surroundings in any given direction of one corner of a unit cell must be identical to the surroundings in the same direction of all the other corners. The corners of the unit cell therefore serve as points which are repeated to form a lattice array
  143. 143. INTERNAL ORDER AND CRYSTAL MORPHOLOGY   Lattice points - corners of the unit cell that serve as points which are repeated to form a lattice array 5 possible lattices in a plane (translation) 1. square unit cell 2. rectangular unit cell 3. centered rectangular unit cell 4. parallelogram 5. hexagonal unit cell - rhombus
  144. 144. BRAVAIS LATTICES    French crystallographer Auguste Bravais (1811-1863) established that in three-dimensional space only fourteen different lattices may be constructed → 6 CRYSTAL SYSTEMS 3 Types of Bravais Lattices:  primitive lattice - has only a lattice point at each corner of the three-dimensional unit cell  body-centered lattice - contains not only lattice points at each corner of the unit cell but also contains a lattice point at the center of the three-dimensional unit cell  face-centered lattice - possesses not only lattice points at the corners of the unit cell but also at either the centers of just one pair of faces or else at the centers of all three pairs of faces
  145. 145. BRAVAIS LATTICES  14 lattices → 6 crystal systems 1. primitive cubic 2. body-centered cubic 3. face-centered cubic 4. primitive tetragonal 5. body-centered tetragonal 6. primitive orthorhombic 7. body-centered orthorhombic 8. single face-centered orthorhombic 9. multiple face-centered orthorhombic 10.primitive monoclinic 11.single face-centered monoclinic 12.primitive triclinic 13.single face-centered hexagonal 14.rhombohedral lattices (rhombohedral lattice is a subset of the hexagonal crystal system)
  146. 146. POINT SYMMETRY   Point symmetry - describes the repetition of a motif or structural feature around a single reference point, commonly the center of a unit cell or a crystal Point Symmetry Operations:  Reflection - structural features on one side of a plane passing through the center of a crystal are the mirror image of the structural features on the other side. The plane across which the reflection occurs is then termed a mirror plane  Rotation - structural element is rotated a fixed number of degrees about a central point and then repeated. A square, for example, possesses 4-fold rotational symmetry because it may be rotated four times by 90° about its central point before it is returned to its original position. Each time it is rotated by 90° the resultant square will be identical in appearance to the original square
  147. 147. POINT SYMMETRY   Point Symmetry Operations:  Inversion - any line which is drawn through the origin at the center of the crystal will connect two identical features on opposite sides of the crystal.  Rotoinversion - compound symmetry operation which is produced by performing a rotation followed by an inversion reflection, rotation, inversion and rotoinversion symmetry operations → combined in different ways → 32 different possible combinations of these symmetry elements → 32 crystal classes → corresponds to a unique set of symmetry operations → each crystal class → placed into one of 6 crystal systems
  148. 148. CRYSTAL SYSTEMS 1. 2. 3. 4. 5. 6. Isometric or cubic Hexagonal 1. hexagonal 2. rhombohedral Tetragonal Orthorhombic Monoclinic Triclinic
  149. 149. CRYSTAL SYSTEMS  ISOMETRIC or CUBIC  the crystallographic axes used in this system are of equal length and are mutually perpendicular, occurring at right angles to one another  all crystals of the isometric system possess four 3-fold axes of symmetry, each of which proceeds diagonally from corner to corner through the center of the cubic unit cell  may also demonstrate up to three separate 4-fold axes of rotational symmetry or six 2-fold axes of symmetry  minerals of this system may demonstrate up to nine different mirror planes  Minerals of this system tend to produce crystals of equidimensional or equant habit  Examples: halite, magnetite and garnet.
  150. 150. CRYSTAL SYSTEMS  ISOMETRIC or CUBIC
  151. 151. CRYSTAL SYSTEMS  HEXAGONAL  minerals of the hexagonal crystal system are referred to three crystallographic axes which intersect at 60° and a fourth which is perpendicular to the other three. This fourth axis is usually depicted vertically.  crystals of the hexagonal division possess a single 6-fold axis of rotation. In addition to the single 6-fold axis of rotation, crystals of the hexagonal division may possess up to six 2-fold axes of rotation. They may demonstrate a center of inversion symmetry and up to seven mirror planes. Crystals of the rhombohedral division all possess a single 3-fold axis of rotation rather than the 6-fold axis of the hexagonal division.  minerals of this division tend to produce hexagonal prisms and pyramids  apatite, beryl and high quartz (hexagonal); calcite, dolomite, low quartz and tourmaline (rhombohedral).
  152. 152. CRYSTAL SYSTEMS  HEXAGONAL
  153. 153. CRYSTAL SYSTEMS  TETRAGONAL  minerals of the tetragonal crystal system are referred to three mutually perpendicular axes. The two horizontal axes are of equal length, while the vertical axis is of different length and may be either shorter or longer than the other two  minerals of this system all possess a single 4-fold symmetry axis. They may possess up to four 2-fold axes of rotation, a center of inversion, and up to five mirror planes  minerals tend to produce short crystals of prismatic habit  zircon and cassiterite
  154. 154. CRYSTAL SYSTEMS  TETRAGONAL
  155. 155. CRYSTAL SYSTEMS  ORTHORHOMBIC  Minerals of the orthorhombic crystal system are referred to three mutually perpendicular axes, each of which is of a different length than the others  Crystals of this system uniformly possess three 2-fold rotation axes and/or three mirror planes. The holomorphic class demonstrates three 2-fold symmetry axes and three mirror planes as well as a center of inversion. Other classes may demonstrate three 2-fold axes of rotation or one 2-fold rotation axis and two mirror planes  Crystals of this system tend to be of prismatic, tabular, or acicular habit  olivine and barite.
  156. 156. CRYSTAL SYSTEMS  ORTHORHOMBIC
  157. 157. CRYSTAL SYSTEMS  MONOCLINIC  Crystals of the monoclinic system are referred to three unequal axes. Two of these axes are inclined toward each other at an oblique angle; these are usually depicted vertically. The third axis is perpendicular to the other two. The two vertical axes therefore do not intersect one another at right angles, although both are perpendicular to the horizontal axis  Monoclinic crystals demonstrate a single 2-fold rotation axis and/or a single mirror plane. The holomorphic class possesses the single 2-fold rotation axis, a mirror plane, and a center of symmetry. Other classes display just the 2fold rotation axis or just the mirror plane  minerals of the monoclinic system tend to produce long prisms  pyroxene, amphibole, orthoclase, azurite, and malachite
  158. 158. CRYSTAL SYSTEMS  MONOCLINIC
  159. 159. CRYSTAL SYSTEMS  TRICLINIC  Crystals of the triclinic system are referred to three unequal axes, all of which intersect at oblique angles. None of the axes are perpendicular to any other axis  Crystals of the triclinic system may be said to possess only a 1-fold symmetry axis, which is equivalent to possessing no symmetry at all. Crystals of this system possess no mirror planes. The holomorphic class demonstrates a center of inversion symmetry  tend to be of tabular habit  plagioclase and axinite
  160. 160. CRYSTAL SYSTEMS  TRICLINIC
  161. 161. CRYSTAL FORMS  Crystal Forms - set of faces which are geometrically equivalent and whose spatial positions are related to one another according to the symmetry of the crystal 1. Monohedron or pedion 2. Parallelohedron or pinacoid 3. Dihedron, or dome 4. Sphenoid 5. Disphenoid 6. Prism 7. Pyramid 8. Dipyramid 9. Trapezohedron 10. Scalenohedron 11. Rhombohedron 12. Tetrahedron 13. 15 under the isometric system
  162. 162. MINERAL CLASSES AND MINERAL IDENTIFICATION
  163. 163. MINERAL CLASSES                 Native elements - eg. Au Sulfides - eg. FeS2 Sulfosalts - eg. Cu3AsS4 Oxides  Simple and multiple - eg. Cu2O  Hydroxides - eg. MnO(OH) Halides - eg. NaCl Carbonates - eg. CaCo3 Nitrates - eg. KNO3 Borates - eg. Na2B4O5(OH)4 ·8H2O) Sulfates - eg. BaSO4 Chromates - eg. PbCrO4 Tungstates - eg. (Fe, Mn)WO 4 Molybdates - eg. PbMoO 4 Phosphates - eg. Ca5(PO4)3(F,Cl,OH) Arsenates - eg. Co3(AsO4)2.2H2O Vanadates - eg. Pb5(VO4)3Cl Silicates - eg. Be3Al2(Si6O18)
  164. 164. BASIS FOR MINERAL CLASSIFICATION    Classification of minerals based on chemical composition Dependent on the dominant anion* or anionic group (eg. oxides, halides, silicates etc.) Reasons for using chemical composition as basis for classification:  Minerals having the same anion or anionic group dominant in their composition have unmistakable family resemblances, in general stronger and more clearly marked than those shared by minerals containing the same dominant cation (eg. Carbonates resemble each other more closely that the minerals of copper)  Minerals related by dominance of the same anion tend to occur together or in the same or similar geologic environment (eg. Sulfides occur in close mutual association in deposits of vein or replacement type, silicates make the bulk of the earth’s rocks)  Agrees well with current chemical practice in naming and classifying inorganic compounds
  165. 165. BASIS FOR MINERAL CLASSIFICATION   Crystallochemical principles – mineral classification must be based on:  Chemical composition  Internal structure Large classes are further divided into subclasses on the basis of internal structure: Silicate class→ { framework silicate subclass (structural { chain silicate subclass (arrangement { sheet silicate subclass (of SiO4 ↓ family (chemical type) ↓ group (structural similarity) ↓ species → series → variety
  166. 166. NATIVE ELEMENTS    ≈ 20 elements in native state (excluding free gasses) Types of Native Elements:  Metals  Semimetals  Nonmetals
  167. 167. NATIVE ELEMENTS  Native Metals  Usefulness of metals arose from the chance discovery of nuggets and masses of gold  Early cultures use metals in native state  Groups of Native Metals: Gold Group Platinum Group Iron Group
  168. 168. NATIVE ELEMENTS  Gold Group  Belong to the same group in the periodic table of elements and have similar chemical properties  Sufficiently inert to occur in an elemental state in nature  Minerals are isostructural and are built on the facecentered lattice  Common Properties: Soft, malleable, ductile and sectile Excellent conductors of heat and electricity Display metallic luster and hackly fracture Have low melting points All are isometric hexoctahedral Have high densities resulting from close cubic packing Gold (Au), silver (Ag), copper (Cu), Lead (Pb)  Differing properties due to atomic properties (specific gravity, color: yellow of Au, red of Cu and white of Ag)
  169. 169. NATIVE ELEMENTS   Platinum Group  Isostructural  Platinum, palladium, iridium, osmium Iron Group  Isostructural  Iron, kamacite, taenite
  170. 170. NATIVE ELEMENTS  Native Semimetals  Arsenic (As), antimony (Sb) and bismuth (Bi)  Belong to an isostructural group with space group R3m  Unlike native metals, these cannot be represented as a simple packing of spheres, because each atom is somewhat closer to three of its neighbors than to the remainder of the surrounding atoms. Bonding of the 4 closest atoms is covalent  Bond type between metallic and covalent, hence, it is stronger and more directional than pure metallic elements  Brittle and much poorer conductors of heat and electricity than the native metals
  171. 171. NATIVE ELEMENTS  Native Non Metals  Sulfur (S), diamond (C) and graphite (C)  Structure very different from the native metals
  172. 172. NATIVE ELEMENTS  GOLD (Au)  Crystallography:  Isometric crystal system  octahedral form  Often in arborescent crystal groups  Crystal are irregularly formed from filiform to reticulated to dendritic  Seldom show crystal forms, often in irregular plates, scales or masses Hardness: 2.5 to 3 Specific Gravity: 19.3 (pure) Fracture: hackly Tenacity: Malleable, ductile Luster: metallic opaque     
  173. 173. NATIVE ELEMENTS    GOLD (Au) Color: various shades of yellow becoming paler with increase in silver Composition and Structure:       Most gold contains Ag When Ag >20% → electrum Small amounts of Cu, Fe and traces of Bi, Pb, Sn, Zn and Platinum metals Purity or “fineness” of gold is expressed in “parts per 1000” Most gold contains about 10% of other metals and has a fineness of 900 Structure of gold is based on cubic closest packing Au  Diagnostic Features:  Distinguished from yellow sulfides pyrite and chalcopyrite and from yellow flakes of altered micas by its sectility and high specific gravity  Fuses at 1063°C  Soluble in aqua regia (1:3 volume HNO3 and HCl  Occurrence:  Rare element but widely distributed in small amounts  Most commonly found in in veins that bear genetic relation to silicic types of igneous rocks
  174. 174. NATIVE ELEMENTS  GOLD (Au)    Most gold occur in native metal If in combination → only with tellurium and selenium Chief source of gold are hydrothermal gold-quartz veins with pyrite and other sulfides deposited from ascending mineral solutions where gold is only mechanically mixed with sulfides and is not in chemical substitution. At or near the surface, of the earth, oxidation of the gold-bearing sulfides sets the gold free, making its extraction easy by amalgamation (finely crushed ore is washed over copper plates coated with mercury)    When sulfides are present in any quantity, not all gold can be recovered by amalgamation → cyanide or chlorination process is used CYANIDATION → finely crushed ore is treated with a solution of potassium or sodium cyanide, forming a soluble cyanide. The gold is then recovered by precipitation with zinc or by electrolysis CHLORINATION → renders gold in a soluble form by treating the crushed and roasted ore with chlorine
  175. 175. NATIVE ELEMENTS  GOLD (Au)  When gold-bearing veins are weathered, the liberated gold either remains in the soil mantle as “eluvial deposit” or is washed into the neighboring streams to form “placer or alluvial gold”. Because of its high specific gravity, gold works its way through the lighter sands and gravels to lodge behind irregularities or in crevices in bedrock. Gold is recovered by panning or washing through sluice boxes where gold collects behind cross-bars and amalgamates with mercury placed behind the cross-bars  Uses: monetary standard, jewelry, scientific instru-ments, electroplating, gold leaf, dental appliances, small gold bars for investment purposes
  176. 176. NATIVE ELEMENTS         SILVER (Ag) Crystallography:  Isometric crystal system  Crystals commonly malformed and in branching arborescent or reticulated groups  Usually in irregular masses, plates and scales, in other places as fine or coarse wires Hardness: 2.5 to 3 Specific gravity: 10.5 (pure) Fracture: hackly Tenacity: Malleable and ductile Luster: metallic Color and streak: silver white and tarnish to brown or gray black
  177. 177. NATIVE ELEMENTS    SILVER (Ag) Composition and Structure:  Frequently contains alloyed Au, Hg, and Cu. Rare traces of Pt, Sb and Bi  Amalgam is a solid solution of Ag and Hg  Structure is based on closest packing of Ag atoms Diagnostic features:  Silver can be distinguished by its malleability, color on fresh surface and high specific gravity  Fusible at 960°C to a bright globule   Occurrence: widely distributed in small amounts in the oxidized zones of ore deposits  Native silver in larger deposits is the result of deposition from primary hydrothermal solutions Uses: photographic film emulsions, plating, brazing alloys, tableware, electronic equipment, coinage
  178. 178. NATIVE ELEMENTS        COPPER (Cu) Crystallography:  Isometric crystal system  Tetrahexahedron, cube, dodecahedron, octahedron  Usually malformed and in branching and arborescent groups  Usually occurs in irregular masses, plates and scales and in twisted wire-like forms Hardness: 2.5 to 3 Specific gravity: 8.9 Fracture: hackly Tenacity: highly malleable and ductile Luster: metallic
  179. 179. NATIVE ELEMENTS    COPPER (Cu) Composition and Structure:  Contains small amounts of Ag, Bi, Hg, As and Sb  Structure is based on cubic closest packing of Cu atoms Diagnostic Features:  Recognized by its red color on fresh surfaces, hackly fracture, high specific gravity and malleability  Fuses at 1083°C to globule  Dissolves readily in nitric acid and the resulting solution is colored deep blue on addition of an excess ammonium hydroxide  Occurrence:  small amounts found in oxidized zones of copper deposits associated with cuprite, malachite and azurite in many localities  Most primary deposits of native copper are associated with basaltic lavas, where deposition of copper resulted from the reaction of hydrothermal solutions with iron oxide minerals  Only major deposit is found in Precambrian basic lava flows in the Keweenaw Peninsula, Michigan
  180. 180. NATIVE ELEMENTS   COPPER (Cu) Use: minor ore of copper, electrical purposes (wires), alloys:  Brass (copper and zinc)  Bronze (copper and tin with zinc)  German silver (copper, zinc and nickel)
  181. 181. NATIVE ELEMENTS         PLATINUM (Pt) Crystallography:  Isometric crystal system  Commonly malformed  Usually in small grains and scales, in some places as irregular masses and nuggets Hardness: 4 to 4.5 (unusually high for metal) Specific Gravity: 21.45 (pure) Tenacity: Malleable, ductile Luster: bright metallic Color: steel gray Composition and Structure:  Usually alloyed with several percent Fe (making it magnetic when iron-rich) and
  182. 182. NATIVE ELEMENTS    PLATINUM (Pt) amounts of Ir, Os, Rh, Pd, Cu, Au, Ni  Structure of platinum is based on the cubic closest packing of Pt atoms Diagnostic Features:  determined by its high specific gravity, malleability, infusibility in the blowpipe flame and insolubility except in aqua regia Occurrence:  most occur as native metal in ultrabasic rocks especially dunites associated with olivine, chromite, pyroxene and magnetite  Occur as placers highly close to the platinum-bearing igneous parent rock First discovered in the United States of Colombia, South America Uses: catalyst in the chemical and petroleum industries, chemical apparatus, electrical equipment, jewelry, dentistry, surgical instruments, pyrometry and photography  
  183. 183. NATIVE ELEMENTS           IRON (Fe) Crystallography:  Isometric crystal system  Crystals are rare  Terrestrial – in blebs and large masses  Meteoric (kamacite) – in plates and lamellar masses Hardness: 4.5 Specific Gravity: 7.3-7.9 Fracture: hackly Tenacity: malleable Luster: metallic opaque Color: steel gray to black Magnetism: strongly magnetic Composition and Structure:  Always contains some Ni and frequently small amounts of Co, Cu, Mn, S and C
  184. 184. NATIVE ELEMENTS    IRON (Fe)  Kamacite contains approx. 5.5. weight percent Ni while Taenite has 27-65 weight percent Ni  Structure is based on bodycentered cubic packing of atoms Diagnostic Features: Strong magnetism, malleability and the oxide coating on its surface. Infusible but soluble in HCLl Occurrence:  Seldom as terrestrial iron but common in meteorites  Elemental iron is highly unstable in oxidizing conditions    Normally present as Fe2+ or Fe3+ in oxides in magnetite (Fe3O4) or hematite (Fe2O3) or goethite (FeO.OH) Terrestrial iron regarded as primary magmatic constituent or a s asecondary product formed from the reduction of iron compounds by assimlated carbonaceous material Most important occurrence is in Disko Is., Greenland
  185. 185. NATIVE ELEMENTS          ARSENIC (As) Crystallography:  Hexagonal crystal system  Pseudocubic crystals rare  Usually granular massive, reniform and stalactitic Cleavage: perfect at {0001} Hardness: 3.5 Specific Gravity: 5.7 Tenacity: brittle Luster: nearly metallic Color: tin-white on fresh fracture, tarnishes to dark gray on exposure Streak: gray     Composition and Structure:  Often shows limited substitution by Sb Diagnostic Features:  Diagnostic blowpipe and chemical tests Occurrence:  Comparatively rare. Found in veins in crystalline rocks associated with Ag, Co, or Ni Uses: very minor ore of arsenic
  186. 186. NATIVE ELEMENTS           BISMUTH (Bi) Crystallography:  Hexagonal crystal system  Distinct crystals are rare  Usually laminated and granular, maybe reticulated or arborescent Cleavage: perfect at {0001} Hardness: 2 to 2.5 Specific Gravity: 9.8 Tenacity: sectile, brittle Luster: metallic Color: reddish silver-white Streak: shining silver-white Composition and Structure:  Small amounts of As, S, Te and As maybe present Structure similar to As and Sb Diagnostic Features:  Recognized chiefly by laminated nature, reddishsilver color, perfect cleavage and sectility  Fusible at 271°C  Diagnostic blowpipe tests Occurrence:  Rare, occurring with ores of Ag, Co, Ni, Pb and Sn Uses: chief ore of bismuth, used for electrical fuses and safety plugs in water sprinkling systems, medicine, cosmetics    
  187. 187. NATIVE ELEMENTS           SULFUR (S) Crystallography:  Orthorhombic crystal system  Pyramidal habit common  Commonly found in irregular masses, massive, reniform, stalactitic Hardness: 1.5 to 2.5 Specific Gravity: 2.05 to 2.09 Fracture: conchoidal to uneven Tenacity: brittle Color: sulfur-yellow, varying with impurities Transparent to translucent Poor conductor of heat When sample is held in hand close to the ear, it can be heard     To crack due to expansion of surface layers due to heat from hand Composition and Structure:  May contain small amounts of Se Diagnostic Features:  Recognized by its yellow color and ease with which it burns  Absence of good cleavage distinguishes it from orpiment  Fusible at 112.8°C and burns with a blue flame with sulfur dioxide  Sublimates in closed tube Occurrence:  Occurs at or near crater rims of active or inactive volcanoes where it is
  188. 188. NATIVE ELEMENTS   SULFUR (S) From the gases given off in fumaroles. These may furnish sulfur as a direct sublimation product or by incomplete oxidation of hydrogen sulfide gas  It is also formed from sulfates, by the action of sulfur-forming bacteria  Maybe found in veins associated with metallic sulfides and formed by the oxidation of the sulfides Uses: chemical industry chiefly in the manufacture of sulfuric acid, fertilizers, insecticides, explosives, coal tar products,  rubber, preparation of wood pulp for paper manufacture
  189. 189. NATIVE ELEMENTS        DIAMOND (C) Crystallography:  Isometric crystal system  Crystals usually octahedral but maybe cubic or dodecahedral  “Bort” variety has rough exterior resulting from radial or cryptocrystalline aggregate (without gem value) Hardness: 10 Cleavage: perfect {111} Specific gravity: 3.51 Luster: adamantine, uncut crystals have a characteristic greasy appearance Color: usually pale yellow or colorless, pale red, green, blue     “Carbonado” is black or grayish black bort, noncleavable, opaque and less brittle than crystals Composition and Structure:  Pure carbon Diagnostic Features:  Hardness, adamantine luster and cleavage  Insoluble in acids and alkalis  At high temperature in oxygen, will burn to CO2 gas leaving no ash Occurrence:  Found in alluvial deposits, where it accumulates because of its inert chemical nature, great hardness and fairly high specific gravity  In Africa and Siberia, they
  190. 190. NATIVE ELEMENTS   DIAMOND (C)  Occur in situ hosted in altered peridotite called kimberlite or “diamond pipes”  First found in India Uses: fragments are used to cut glass, grinding and polishing diamonds and other gemstones, cutting rocks, diamond drilling, gemstones-value depends on the color and purity, skill by which it was cut and its size (1 carat=0.2 g.)
  191. 191. NATIVE ELEMENTS            GRAPHITE (C) Crystallography:  Hexagonal crystal system  Usually tabular Hardness: 1-2 (readily marks paper and soils fingers) Specific Gravity: 2.23 Fracture: hackly Luster: metallic to dull Color: black Streak: black Greasy feel Composition and Structure:  Carbon Diagnostic Features:  Color, foliated nature and greasy feel, unattacked by acids, infusible but may burn to CO2   Occurrence:  Mostly occurs in metamorphic rocks such as marble, gneiss and schist derived from the carbonaceous material of organic origin that has been converted into graphite during metamorphism. Metamorphosed coal beds may be partially converted into graphite during metamorphism Uses: manufacture of refractory crucibles for steel, brass and bronze industries, lubricant (mixed with oil) pencil lead (mixed with fine clay, protective paint for structural steel, batteries, electrodes and generator brushes
  192. 192. NATIVE ELEMENTS   GRAPHITE (C) Uses: manufacture of refractory crucibles for steel, brass and bronze industries, lubricant (mixed with oil) pencil lead (mixed with fine clay, protective paint for structural steel, batteries, electrodes and generator brushes
  193. 193. SULFIDES      An important class of minerals that includes the majority of the ore minerals Sulfide class also includes the sulfarsenides, arsenides and tellurides Most sulfides are opaque with distinctive colors and characteristic colored streaks General formula of sulfides is XmZn in which X represents the metallic elements and Y the nonmetallic element Many of the sulfides have ionic and covalent bonding whereas others, displaying most of the properties of metals, have metallic bonding
  194. 194. SULFIDES           ACANTHITE (Ag2S) Crystallography:  Monoclinic crystal system  Crystals commonly cubic  Most commonly massive or as coating Hardness: 2 to 2.5 Specific Gravity: 7.3 Tenacity: very sectile, can be cut by a knife like lead Luster: metallic Color: black Streak: black, shining Bright on fresh surface but on exposure becomes dull black, owing to the formation of an earthy sulfide also known as ARGENTITE    Composition and Structure:  Ag (87.1%), S (12.9%), commonly contains impurities such as calcium and magnesium sulfates and calcium and magnesium chlorides Diagnostic Features:  Distinguished by its color, sectility and high specific gravity Occurrence:  An important primary silver mineral found in veins associated with native silver, the ruby silvers, galena and sphalerite
  195. 195. SULFIDES  ACANTHITE (Ag2S)  May also occur of secondary origin Uses: important ore of silver 
  196. 196. SULFIDES            CHALCOCITE (Cu2S) Crystallography:  Orthorhombic crystal system  Crystals are very rare  Commonly fine-grained and massive Cleavage: poor {110} Fracture: conchoidal Hardness: 2.5 to 3 Specific Gravity: 5.5 to 5.8 Tenacity: imperfectly sectile Luster: metallic Color: shining lead gray tarnishing to dull black on exposure Streak: grayish black Some chalcocite are soft and sooty    Composition and Structure:  Cu (79.8%), S (20.0%), may contain small amounts of Ag and Fe Diagnostic Features:  Distinguished by its lead gray color and sectility. When heated on charcoal it gives odor of SO2 Occurrence:  One of the most important copper-ore mineral  Principal occurrence is as a supergene mineral in enriched zones of sulfide deposits (under surface conditions the primary copper sulfides are oxidized
  197. 197. SULFIDES  CHALCOCITE (Cu2S)    The soluble sulfates formed above move downward reacting with the primary minerals to form chalcocite and thus enriching the ore in copper. The water table is the lower limit of the zone of oxidation and here a chalocite blanket may form) May also occur as primary mineral in in veins with bornite, chalcopyrite, enargite and pyrite Much of the world’s copper is produced from “porphyry copper”. In porphyry copper, primary copper minerals are disseminated through the rock  Uses: important ore of copper

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