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  1. 1. Mineralogy Unit-II
  2. 2. Syllabus • Introduction of Minerals and Crystals, Mode of Formation of Minerals, Common Rock forming Minerals and their abundance, Different method of study of minerals, Significance of different physical properties in mineral Identification, diagnostic Physical Properties.
  3. 3. What is a Mineral? • Definition: a 1homogeneous, 2naturally-occurring, 3solid, and 4 generally inorganic substance with a 5definable chemical composition and an 6orderly internal arrangement of atoms • Does not include “minerals” in the nutritional sense
  4. 4. 1- Homogeneous  Definition: Something that is the same through and through Cannot be broken into simpler components 2- Naturally Occurring  Minerals are the result of natural geological processes  Man-made minerals are called synthetic minerals (e.g. industrial diamonds) 3- Solid  Minerals must be able to maintain a set shape nearly indefinitely  liquids are not minerals
  5. 5. 4- Definable Chemical Composition  A mineral can be described by a chemical formula  Quartz: SiO2  Biotite: K(Mg, Fe)3 (AlSi3O10)(OH)2  Diamond: C 5- Orderly Arrangement of Atoms • Minerals have a fixed atomic pattern that repeats itself over a large region relative to the size of atoms – Crystal solid, or crystal lattice: The organized structure of a mineral – A glass is not a mineral; no organized structure 6- Generally Inorganic • Organic: A substance composed of C bonded to H, with varying amounts of O, N and other elements. C, alone, is not organic! • Only a few organic substances are considered minerals, all other minerals are inorganic
  6. 6. Mineralogy A mineral is a naturally occurring substance that is solid and stable at room temperature, representable by a chemical formula, and has an ordered atomic structure. It is different from a rock, which can be an aggregate of minerals or non-minerals, and does not have a specific chemical composition. The study of minerals is called mineralogy. There are over 4,900 known mineral species; over 4,660 of these have been approved by the (IMA). International Mineralogical Association
  7. 7. Crystals • Crystals • Minerals bounded by smooth (planar) surfaces (faces) that are arranged in a symmetrical fashion. • Planar surfaces or faces are manifestations of the internal structure of the mineral, which is a function of the unique arrangement of atoms in each mineral.
  8. 8. Crystals • In the 1600s, scientists realized that crystals are: • Composed of small building blocks (unit cells). • These blocks are added in a regular way thus creating the crystal. • Each „block‟ or „unit cell‟ contains a small number of atoms. • Each „block‟ or „unit cell‟ has the same atomic composition. • The „block‟ or „unit cell‟ has the same shape and symmetry (form) as the entire crystal (sort of intuitive).
  9. 9. NaCl Crystals
  10. 10. Crystals • Regular geometric solid bounded by smooth plane surfaces, characterized by ordered arrangement of atoms. • Every atom within a crystal contains an identical environment. • The atoms can be related to one another by geometrical operations – symmetry operations.
  11. 11. Organized Crystal Lattice • Glass: no organized molecular structure • Minerals: organized molecules • Example: Quartz – Although different crystals may look different, they share certain consistent characteristics
  12. 12. Identifying Crystal Structures • Some mineralogists use x-ray diffraction patterns to identify minerals.
  13. 13. X-ray diffraction: Laue photographic method
  14. 14. Seeing Into Crystals  Modern instrumentation allows us to “see” atoms.  A beam of electrons passes through material.  Atoms scatter electrons, which pass between them.  A shadow on the detector indicates a row of atoms.  This principle drives the electron microscope.
  15. 15. Crystal • Occurance of complete and independent crystals are rare in nature. Good crystals develop only under favorable conditions such as • Slow cooling (i.e.. Slow crystallization) • Free surrounding to facilitate the crystal growth in different directions. • Non interference by the adjacent growing minerals during solidification. In nature more than 99 % of minerals are crystalline and only few are amorphous
  16. 16. Crystals
  17. 17. Crystal Characteristics of Crystal • The following are some of the details relating to crystals and minerals • Faces: The crystals are bounded by flat surfaces which are known as faces. • Edge: the line of intersection formed by three or more adjacent faces in a crystal are called solid angles. • Solid angles: The point of intersection formed by three or more adjacent faces in a crystal are called as solid angles.
  18. 18. Faces , Edges of crystals
  19. 19. Crystal Distortion • In spite of perfect internal atomic arrangement, sometimes crystals develop faces of different sizes and shapes. This kind of geometrical irregularities in the shape is called “ Distortion”. Interfacial Angle In crystallography, interfacial angle is the angle formed in between the normal of adjacent crystal faces.
  20. 20. Distortion & Interfacial Angles
  21. 21. Crystal • Simple form and combination • If a crystal is bounded by all similar or like faces it is called a simple form. If the crystal is bounded by dissimilar faces it is called as combination. • Crystallographic axes • These are imaginary lines which interact at the centre of crystal. The growth or development of the crystal is considered to take place along the axes.
  22. 22. Crystals
  23. 23. Crystal • Crystal Systems • The six possible crystal systems are cubic system, tetragonal system, hexagonal system, orthorhombic system, monoclinic system and triclinic system
  24. 24. Crystal Systems
  25. 25. Mode of formation of minerals • Basically there are three kinds of formation of minerals in nature. They are formed from magma or out of secondary processes or under metamorphism. • Most of the minerals are formed directly or indirectly out of magma during different stages of its solidification. Important and bulky rock- forming minerals such as feldspar, quartz, pyroxenes, amphiboles, micas, are formed these ways. • Some precious minerals such as garnet, topaz, magnetite are also formed from magmatic sources.
  26. 26. Mode of formation of Minerals
  27. 27. Mode of formation of Minerals • In nature, some minerals are formed from secondary processes like weathering, precipitation and deposition. Minerals like calcite, dolomite, salts, coal, are example of this group. • Another important mode of formation of minerals is out of metamorphism. These minerals are formed under the influence of high temperature and pressure with or without active involvement of chemically active solutions.
  28. 28. Common Rock forming Minerals • Based on their nature and economic importance, all minerals are grouped into „ rock forming minerals” (e.g. feldspar, quartz, biotite mica) and „economic minerals ‟ some economic minerals by virtue of their physical properties serves as a source of extraction of valuable metals. based on this minerals are groups as metallic minerals (hematite, galena, chromium, etc) and non- metallic minerals (asbestos, graphite, and megnasite).
  29. 29. Civil Engineering Importance of Rock forming minerals • Undoubtly, among different minerals of economic minerals by virtue of their utility and inherit values are very important. However from civil engineering point of view, rock forming minerals are very essential because • The civil engineers need to know the properties of rocks precisely to enable them to consider different rocks for any required purpose i.e. as a foundation rock, as a road metal, as concrete aggregate, as building stones, as floorings, or roofing minerals as decorative material.
  30. 30. Civil Engineering Importance of Rock forming minerals • Thus properties of rocks such as strength, durability, and appearance of rock can be assessed only with knowledge of the minerals that form rock. The economic minerals , since they are scare, do not influence the properties of rocks and hence irrelevant from civil engineering point of view.
  31. 31. Different methods of study of minerals • According to the definition, every mineral has its own chemical composition and atomic structure. This combination of chemical composition and atomic structure is unique for every minerals. This in fact facilitates the study of minerals in different ways. Common methods of study and identification of minerals are • (i) Their physical properties • (ii) Their chemical composition • (iii) Optical methods • (iv) X-ray analysis
  32. 32. Study of Physical Properties • Physical properties of minerals like color, shine, hardness, density,etc can be studied with mere observation of small mineral specimen. • Since the minerals invariably possess its own specific chemical composition and atomic structure every minerals should possess its own physical properties.
  33. 33. Study of Chemical Composition • According to the definition, every mineral is expected to have its own distinctive chemical composition, which is not to be found in any other mineral. Therefore, by chemical analysis, if the composition is known it should be possible to identify the minerals
  34. 34. Study of Chemical Composition
  35. 35. Study of Optical Properties • In this method of study, the minerals are ground very fine and fixed over glass slides. They are studied under petrological microscope. Different optical properties are studied under polar microscope. The properties of minerals like, color, relief, cleavage, shape and pleochroism are studied under polarized light.
  36. 36. Seeing Into Crystals
  37. 37. Study of Optical Properties • The principle which makes this method useful for study and identification of minerals is that when polarized light passes through thin sections of minerals it is influenced in a characteristic way depending on the chemical composition and atomic structure of the minerals.
  38. 38. Study of Optical Properties
  39. 39. X-ray Analysis • X-ray analysis makes use of the definite atomic structure, found in every mineral. X-ray are similar to light wave but have a much shorter wavelength, comparable to the distance between atom in a crystalline mineral.
  40. 40. X-ray Analysis • When a beam of x-ray falls on a crystal, it is diffracted by the layers of atoms within a crystal, in making an x-ray analysis of the atomic structure of the crystal, the diffracted x- rays are allowed to fall on a photographic plate, and the resulting photograph shows a series of spots or lines which form more or less symmetrical pattern. Thus x-ray analysis of minerals reveal their actual atomic structure, which is distinctive for each minerals. This enables the accurate identification of minerals.
  41. 41. Identifying Crystal Structures • Some mineralogists use x-ray diffraction patterns to identify minerals.
  42. 42. X-ray diffraction: Laue photographic method
  43. 43. Minerals : Physical Properties and Crystal Forms From: http://webmineral.com/data/Rhodochrosite.shtml
  44. 44. The Physical properties of minerals are used by Mineralogists to help determine the identity of a specimen. Some of the tests can be performed easily in the field, while others require laboratory equipment. For the beginning student of geology, there are a number of simple tests that can be used with a good degree of accuracy. The Physical Properties of Minerals
  45. 45. The Physical Properties of Minerals • Color • Streak • Luster • Hardness • External Crystal Form • Cleavage
  46. 46. The Physical Properties of Minerals (cont.) • Fracture • Specific Gravity • Special Properties • Degree of Transparency • Other Properties • Chemical Tests
  47. 47. Mineral Identification • Since we can‟t all have x-ray diffraction machines and electron microscopes, we identify minerals by visual and chemical properties called physical properties. • Types of physical properties that geologists use include: – Color, Streak, Luster, Hardness, Specific Gravity, Crystal Habit, and Cleavage Pyrite  Properties depend upon…  Chemical composition.  Crystal structure.  Some are diagnostic.  Minerals have a unique set of physical properties.
  48. 48. 1- Color • Color may be diagnostic for a few minerals, but in general, a given mineral can have a range of colors. Various colors of quartz, SiO2 Hematite (Fe2O3) can have various colors, but its streak is always red-brown 2- Streak  The color of the pulverized powder of a mineral.  More consistent than color  Found by scraping a mineral against a porcelain plate
  49. 49. Important Physical Properties • Color - Although an obvious feature, it is often unreliable to use to determine the type of mineral.  Color arises due to electronic transitions, often of trace constituents, in the visible range of the EM spectrum. For example, quartz is found in a variety of colors. • Color of a mineral may be quite diagnostic for the trace element and coordination number of its bonding environment.
  50. 50. Hope Diamond: 44.5 carats http://www.nmnh.si.edu/minsci/hope.htm
  51. 51. Color • Colour : Colour is the first thing someone notices when they view a mineral. Color is also one of the big reasons that attract people to minerals. Generally speaking, color is not a good property to be used in the identification of minerals. It is usually the first property to confuse a novice collector into making an incorrect identification. • Minerals having Property of Green, Golden Yellow, Yellow, White, Red, Blue, Black, Grey, Purple & Transparent Colour.
  52. 52. Color
  53. 53. Color
  54. 54. Important Physical Properties • Streak - The color of a mineral in its powdered form; obtained by rubbing the mineral against an unglazed porcelain plate. • Streak is usually less variable than color. • Useful for distinguishing between minerals with metallic luster.
  55. 55. Streak
  56. 56. 3- Luster • The way a mineral‟s surface scatters light Metallic luster 4- Hardness • The measure of a mineral to resist scratching • Represents the strength of bonds in the crystal lattice – Measured on a qualitative scale called Mohs Hardness Scale Nonmetallic luster Vitreous luster (Nonmetallic) Adamantine luster (Nonmetallic)
  57. 57. Important Physical Properties • Luster - This property describes the appearance of reflected light from the mineral's surface. Nonmetallic minerals are described using the following terms: vitreous, pearly, silky, resinous, and earthy.
  58. 58. Luster Lustre is a description of the way a mineral surface looks when light reflects off of the surface.
  59. 59. Luster
  60. 60. Important Physical Properties • Hardness - This is the resistance of the mineral to abrasion or scratching. This property doesn't vary greatly from sample to sample of the same mineral, and thus is highly diagnostic. It also is a direct reflection of the bonding type and internal atomic arrangement. A value is obtained by comparing the mineral to a standard scale devised by Moh, which is comprised of 10 minerals ranging in hardness from talc (softest) to diamond (hardest).
  61. 61. Mohs’ Hardness Scale
  62. 62. Hardness • The hardness of a mineral is a way of describing how easy or difficult it is to scratch the mineral. It is used, in combination with the other physical properties, to help identify a mineral specimen
  63. 63. Mohs scale of mineral hardness • The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. • It was created in 1812 by the German geologist and mineralogist Friedrich Mohs.
  64. 64. Mohs scale of mineral hardness
  65. 65. Mohs scale of mineral hardness • The Mohs scale of mineral hardness is based on the ability of one natural sample of matter to scratch another mineral. The samples of matter used by Mohs are all different minerals. Minerals are pure substances found in nature. Rocks are made up of one or more minerals. As the hardest known naturally occurring substance when the scale was designed, are at the top of the scale. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, and/or the softest material that can scratch the given material.
  66. 66. Mohs scale of mineral hardness
  67. 67. Mineral Hardness The Moh's Scale of Hardness: Talc Gypsum Calcite Fluorite Apatite Orthoclase Feldspar
  68. 68. Mineral Hardness The Moh's Scale of Hardness: Quartz Topaz Corundum Diamond
  69. 69. Moh’s Hardness Scale • Fingernail = 2.5 • Glass = 5.5 • Streak Plate = 6.5 • Talc =1 • Quartz = 7 • Diamond = 10 This doesn’t mean that diamonds are 10 times harder than talc… that’s why we call this a qualitative measure, not quantitative measure
  70. 70. 5- Specific Gravity  Specific Gravity: The weight of a substance divided by the weight of an equal volume of water 6- Crystal Habit • A description of a mineral‟s consistent shape Prismatic Blade-like or Elongated Needle-like or fibrous
  71. 71. Density and Specific Gravity • Density - Defined as the mass divided by the volume and normally designated by the Greek letter, rho, Mass/ Volume; SI units: kg/m3 or kg m-3, but geologists often use g/cm3 as the unit of choice. • Specific Gravity - Ratio of the mass of a substance to the mass of an equal volume of water. S.G. is unit-less. • Examples - quartz (SiO2) has a S.G. of 2.65 while galena (PbS) has a S.G. of 7.5 and gold (Au) has a S.G. of 19.3.
  72. 72. Specific Gravity • Specific Gravity : Specific Gravity of a mineral is a comparison or ratio of the weight of the mineral to the weight of an equal amount of water. The weight of the equal amount of water is found by finding the difference between the weight of the mineral in air and the weight of the mineral in water.
  73. 73. Specific Gravity • Specific Gravity (G) = mass of subs./mass of equiv. Vol. H2O at 4ºC • Silicates ~ 2.5 • Gold ~ 19 • Galena ~ 7.5 • 45 • Specific Gravity is a „way‟ of expressing density. • Density: weight/unit volume (g/cm3)
  74. 74. Important Physical Properties • Crystal form or habit - The external morphology of crystals generally reflect the internal arrangement of their constituent atoms. This can be obscured, however, if the mineral crystallized in an environment that did not allow it to grow without significant interaction with other crystals (even of the same mineral).
  75. 75. External Crystal Form • Crystal structure results from the orderly geometric spatial arrangement of atoms in the internal structure of a mineral. This crystal structure is based on regular internal atomic or ionic arrangement that is often expressed in the geometric form that the crystal takes. Even when the mineral grains are too small to see or are irregularly shaped, the underlying crystal structure is always periodic and can be determined by X-ray diffraction.
  76. 76. Crystal Form  Crystal form is the external expression of the internally ordered arrangement of atoms.  During mineral formation, individual crystals develop well-formed crystal faces that are specific to that mineral.  The crystal faces for a particular mineral are characterized by a symmetrical relationship to one another that is manifest in the physical shape of the mineral‟s crystalline form.  Crystal forms are commonly classified using six different crystal systems, under which all minerals are grouped. 1. Isometric (Cubic) 2. Tetragonal 3. Orthorhombic 4. Hexagonal 5. Monoclinic 6. Triclinic The six major crystal forms: Axes and Angles C BA  
  77. 77. Crystal Form, cont.  Isometric: Isometric crystals are block shaped with relatively similar and symmetrical faces. The crystal form has three axes all at 90° angles and all the same length. Mineral Example: Pyrite Tetragonal: Tetragonal crystals are shaped like four-sided pyramids or prisms. The crystal form has three axes that are all perpendicular to one another. Two axis have the same length, and one is different. The axes that are the same length lie on a horizontal plane, with the third axis at a right angle to the other two. Mineral Example: Zircon Orthorhombic: Orthorhombic crystals are shaped like a rectangular prism with a rectangular base. The crystal has three axes of different lengths and intersect at 90° angles. Mineral Example: Topaz Copyright© Dr. Richard Busch Isometric: Pyrite Tetragonal: Zircon Copyright© Dr. Richard Busch Axes Length Relationships: A = B = C Angles:  =  =  = 90 A C B A B C Axes Length Relationships: A  B  C Angles:  =  =  = 90 C BA Axes Length Relationships: A  B  C Angles:  =  =  = 90 Orthorhombic: Topaz Photo Courtesy USGS77 Table of Contents C BA  
  78. 78. Crystal Form, cont. Hexagonal: Hexagonal crystals have three symmetrical axes that occur in the same plane and are all the same length. The fourth axis may be either longer or shorter, and it intersects the other three axis at 90° angles. The sides intersect at 120 ° angles. Mineral Example: Amethyst Monoclinic: Monoclinic crystals are short and stubby with tilted faces. Each crystal has three axes that are unequal. Two of the axes lie in the same plane at right angles to each other, the third axis is inclined. Mineral Example: Gypsum Triclinic: Triclinic crystals have three axis which are all different lengths and all three axis intersect at angles other than 90°. Mineral Example: Kyanite Monoclinic: Gypsum Copyright © Stonetrust ,Inc. A B D C A B C A B C Axes length Relationships: A = B = C ≠ D Angles:  =  = 90 and  = 120 Axes Length Relationships: A ≠ B ≠ C Angles:  ≠  ≠  Axes Length Relationships: A ≠ B ≠ C Angles:  ≠  =  = 90 Hexagonal: Amethyst Copyright © Stonetrust ,Inc. Triclinic: Kyanite Copyright © Stonetrust ,Inc. C BA  
  79. 79. Chrysotile Asbestos Belongs to the Serpentine mineral family - hydrated ferromagnesian silicate.
  80. 80. Feldspar
  81. 81. Intergrown cubic crystals of fluorite
  82. 82. Quartz Interfacial Angles Perfectly Proportioned Crystals Misshapen Crystals Steno’s Law (1669): Crystal face internal angles remain constant!
  83. 83. Macroscopic Forms and Microscopic Blocks Cubes Rhombs Macroscopic Crystal Forms
  84. 84. Unit Cells and Crystal Structure Cubic unit cell: smallest repeatable unit
  85. 85. Fracture and Cleavage • Cleavage: The tendency of a mineral to break along a plane of weakness in the crystal lattice. • Fracture: The mineral breaks in no consistent manner – Equal bond strength in all directions • Conchoidal Fracture: The tendency for a mineral to break along irregular scoop-shaped fractures that are not related to weaknesses in the crystal structure Obsidian, a volcanic glass, and quartz commonly exhibit conchoidal fracture, which is why Indians used them as cutting tools.
  86. 86. Important Physical Properties • Cleavage - Orientation and number of planes of weakness within a mineral. Directly reflects the orientation of weak bonds within the crystal structure. This feature is also highly diagnostic. • Fracture - This describes how a mineral breaks if it is not along well defined planes. In minerals with low symmetry and highly interconnected atomic networks, irregular fracture is common.
  87. 87. Planer Cleavage in Mica
  88. 88. Weak Bonding Yields Planer Cleavage
  89. 89. Amphibole Cleavage ~120/60°
  90. 90. Rhombohedra Cleavage in Calcite
  91. 91. Cleavage • Tendency to break along planes of weakness. • Cleavage produces flat, shiny surfaces. • Described by number of planes and their angles. • Sometimes mistaken for crystal habit. – Cleavage is through-going; often forms parallel “steps.” – Crystal habit is only on external surfaces. • 1, 2, 3, 4, and 6 cleavage planes possible.
  92. 92. Cleavage  Examples of Cleavage:  1 direction  2 directions at 90º  2 directions NOT at 90º Muscovite Mica Amphibole Potassium Feldspar
  93. 93.  Examples of Cleavage:  3 directions at 90º  3 directions NOT at 90º Cleavage Calcite Halite
  94. 94. Cleavage • Cleavage - Cleavage is the tendency of minerals to break along preferred directions. Some minerals tend to have one direction of cleavage.
  95. 95. Cleavage
  96. 96. Fracture • Fracture - Fracture represents a mineral break other than along a cleavage or parting plane. Breaks may occur in any direction but are usually around some imperfection in the mineral.
  97. 97. Fracture
  98. 98. Conchoidal Fracture in Glass
  99. 99. Degree of Transparency • This is also known as „ diaphaneity‟ depending upon the resistance offered by the minerals to the passage of light though them, they may be classified as transparent ( rock crystal, ice landspar) Translucent (calcite, agate) and opaque (galena, ilmenite, pyrite) .
  100. 100. Degree of Transparency • This character of a mineral depends on the chemical composition, impurities present, inclusions, weathering, and also on thickness. Rock forming minerals usually appear opaque, when they are thick, but they lose this opaque character if they are made thinner
  101. 101. Special Characteristics • There are other special characteristics that some minerals exhibit that allow us to identify them – Reacts to Acid [Calcite and Dolomite: CaCO3 & Ca(Mg)CO3] – Magnetic [Magnetite: Fe3O4] – Salty taste [Halite: NaCl] – Striations [Plagioclase Feldspar: NaAlSi3O8 - CaAl2Si2O8, Pyrite - FeS2, Quartz - SiO2] Striations on Pyrite Calcite reacts with HCl and gives off CO2
  102. 102. Special and Other Properties • Striations - Commonly found on plagioclase feldspar. Straight, parallel lines on one or more of the cleavage planes caused by mineral twinning. • Magnetism - Property of a substance such that it will spontaneous orient itself within a magnetic field. Magnetite (Fe3O4) has this property and it can be used to distinguish it from other non-magnetite iron oxides, such as hematite (Fe2O3). • Double Refraction - Seen in calcite crystals. Light is split or refracted into two components giving rise to two distinct images.
  103. 103. Plagioclase striations Striations
  104. 104. Striations
  105. 105. Double Refraction
  106. 106. Double Refraction
  107. 107. Thanks !