Chapter 3 minerals


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Chapter 3 minerals

  1. 1. Essentials of Geology 3 rd Edition Chapter 3 Norton Media Library
  2. 2. Patterns in Nature: Minerals Prepared by: Ronald Parker , Senior Geologist Fronterra Geosciences Houston, Oklahoma City, Denver, Anchorage, Dallas, Midland, Aberdeen, Vienna, Buenos Aires, Neuquén
  3. 3. Minerals <ul><li>Minerals are the “building blocks” of rocks—hence, Earth. </li></ul><ul><li>More than 4,000 are known. </li></ul><ul><li>Dozens of new minerals are discovered annually. </li></ul><ul><li>Human interest in minerals spans millenia. </li></ul>
  4. 4. Minerals <ul><li>Developed societies depend on mineral resources. </li></ul><ul><ul><li>Metals – Iron, copper, lead, zinc, nickel, aluminum, etc. </li></ul></ul><ul><ul><li>Non-metals – Gypsum, limestone, aggregate, clay. </li></ul></ul>
  5. 5. Minerals <ul><li>Economically important – Drive world economies. </li></ul><ul><li>Historically important – Dictated human history. </li></ul><ul><ul><li>Iron. </li></ul></ul><ul><ul><li>Copper. </li></ul></ul><ul><ul><li>Gold. </li></ul></ul><ul><ul><li>Diamonds. </li></ul></ul><ul><ul><li>Gems. </li></ul></ul>Figure 3.2b Figure 3.1 Figure 3.2a
  6. 6. Mineral Definition <ul><li>Geologic definition of a mineral is specialized: </li></ul><ul><ul><li>Naturally occurring. </li></ul></ul><ul><ul><li>Solid. </li></ul></ul><ul><ul><li>Definite chemical </li></ul></ul><ul><ul><li>composition. </li></ul></ul><ul><ul><li>Ordered atomic </li></ul></ul><ul><ul><li>arrangement. </li></ul></ul><ul><ul><li>Mostly inorganic. </li></ul></ul><ul><li>A mineraloid exhibits some of these properties. </li></ul><ul><li>Doesn’t include “minerals” in the nutritional sense. </li></ul>
  7. 7. Rocks <ul><li>Rocks are earth materials made from minerals. </li></ul><ul><li>Most rocks contain more than one kind of mineral. </li></ul><ul><ul><li>Example: Granite </li></ul></ul><ul><ul><ul><li>K-feldspar – Pink. </li></ul></ul></ul><ul><ul><ul><li>Quartz – Gray. </li></ul></ul></ul><ul><ul><ul><li>Hornblende – Black. </li></ul></ul></ul><ul><li>Some are monomineralic. </li></ul><ul><ul><li>Limestone (Calcite) </li></ul></ul><ul><ul><li>Rock salt (Halite) </li></ul></ul><ul><ul><li>Glacial ice. </li></ul></ul>
  8. 8. Crystalline Structure <ul><li>Atoms in a mineral are specifically ordered. </li></ul><ul><li>A solid with disordered atoms is called a glass. </li></ul><ul><li>Crystalline structure is based on atomic patterns. </li></ul>
  9. 9. Crystals <ul><li>Rare minerals displaying flat external faces. </li></ul><ul><li>Crystal faces form best in open cavities. </li></ul><ul><li>Crystals are often prized mineral specimens. </li></ul>
  10. 10. Crystals <ul><li>Constancy of interfacial angles. </li></ul><ul><ul><li>Different samples of the same mineral will have the same crystal faces. </li></ul></ul><ul><ul><li>Adjacent faces are always </li></ul></ul><ul><ul><li>oriented at the same angle. </li></ul></ul><ul><li>Crystal faces reflect the </li></ul><ul><li>internal atomic order. </li></ul>
  11. 11. Crystal Lattice <ul><li>Ordered atoms in crystals form a 3-D lattice. </li></ul><ul><li>Lattices are patterns that repeat in three dimensions. </li></ul><ul><li>This internal pattern controls most mineral properties. </li></ul><ul><ul><li>Crystal shape. </li></ul></ul><ul><ul><li>Symmetry. </li></ul></ul>
  12. 12. Atomic Bonding <ul><li>Lattice atoms are held in place by atomic bonds. </li></ul><ul><li>Bond characteristics also govern mineral properties. </li></ul><ul><li>Models depict atoms, bonds, and lattices. </li></ul>
  13. 13. Polymorphs <ul><li>Minerals with the same composition; different structure. </li></ul><ul><li>Polymorphs reveal the importance of bond type. </li></ul><ul><li>Diamond and graphite are carbon polymorphs (C). </li></ul><ul><ul><li>Diamond – Strong covalent bonds; hardest mineral. </li></ul></ul><ul><ul><li>Graphite – Weak van der Waals bonds; softest mineral. </li></ul></ul>Graphite Diamond
  14. 14. Crystal Growth <ul><li>Crystals grow as atoms attach to mineral surfaces. </li></ul><ul><li>Growth starts from a central seed crystal. </li></ul><ul><li>Growth expands outward as atoms accumulate. </li></ul>
  15. 15. Crystal Growth <ul><li>Outward crystal growth fills available space. </li></ul><ul><li>Resulting crystal shape is governed by surroundings. </li></ul><ul><ul><li>Open space – Good crystal faces grow. </li></ul></ul><ul><ul><li>Confined space – No crystal faces. </li></ul></ul><ul><li>Crystals grow by… </li></ul><ul><ul><li>Solidification from a melt. </li></ul></ul><ul><ul><li>Precipitation from solution. </li></ul></ul><ul><ul><li>Solid-state diffusion. </li></ul></ul>
  16. 16. Mineral Physical Properties <ul><li>Characteristics determined by your five senses. </li></ul><ul><li>Used to ID minerals. </li></ul><ul><li>Properties depend upon… </li></ul><ul><ul><li>Chemical composition. </li></ul></ul><ul><ul><li>Crystal structure. </li></ul></ul><ul><li>Some are diagnostic. </li></ul><ul><li>Example: Pyrite (FeS 2 ) </li></ul><ul><li>Cubic crystals, high specific gravity, striated crystal faces, black streak, metallic luster, dull brassy color, sulfur smell when crushed, erroneously mistaken for gold (fool’s gold). </li></ul><ul><li>Minerals have unique sets of physical properties. </li></ul>Pyrite
  17. 17. Mineral Physical Properties <ul><li>Common properties of </li></ul><ul><li>minerals are... </li></ul><ul><ul><li>Crystal form. </li></ul></ul><ul><ul><li>Crystal habit. </li></ul></ul><ul><ul><li>Luster. </li></ul></ul><ul><ul><li>Color. </li></ul></ul><ul><ul><li>Streak. </li></ul></ul><ul><ul><li>Hardness. </li></ul></ul><ul><ul><li>Cleavage. </li></ul></ul><ul><ul><li>Fracture. </li></ul></ul><ul><ul><li>Specific gravity. </li></ul></ul>Needle-like crystal habit
  18. 18. Mineral Physical Properties <ul><li>Less common physical properties are... </li></ul><ul><ul><li>Taste. </li></ul></ul><ul><ul><li>Smell. </li></ul></ul><ul><ul><li>Feel. </li></ul></ul><ul><ul><li>Elasticity. </li></ul></ul><ul><ul><li>Magnetism. </li></ul></ul><ul><ul><li>Effervescence. </li></ul></ul><ul><ul><li>Diaphaneity. </li></ul></ul><ul><ul><li>Piezoelectricity. </li></ul></ul><ul><ul><li>Pyroelectricity. </li></ul></ul><ul><ul><li>Refractive index. </li></ul></ul><ul><ul><li>Malleability. </li></ul></ul><ul><ul><li>Ductility. </li></ul></ul><ul><ul><li>Sectility. </li></ul></ul>Calcite effervesces with acid Magnetite crystals on a large magnet.
  19. 19. Color <ul><li>Color is diagnostic for some minerals. </li></ul><ul><ul><li>Olivine is olive green. </li></ul></ul><ul><ul><li>Azurite is always blue. </li></ul></ul><ul><li>Some minerals may exhibit a broad color range. </li></ul><ul><ul><li>Quartz (Clear, white, yellow, pink, purple, gray, etc). </li></ul></ul><ul><li>Color varieties often reflect trace impurities. </li></ul>Quartz – Many colors Malachite – Always green
  20. 20. Streak <ul><li>Mineral color crushed on an unglazed porcelain plate. </li></ul><ul><li>Streak is often a useful diagnostic property. </li></ul><ul><ul><li>Congruent streak – Streak color the same as the mineral. </li></ul></ul><ul><ul><ul><li>Magnetite – Black mineral; black streak. </li></ul></ul></ul><ul><ul><li>Incongruent streak – Streak color differs from the mineral. </li></ul></ul><ul><ul><ul><li>Chromite – Black mineral; greenish-brown streak. </li></ul></ul></ul>Hematite – Red-brown streak
  21. 21. Luster <ul><li>The way a mineral surface scatters light. </li></ul><ul><li>Two subdivisions. </li></ul><ul><ul><li>Metallic – Looks like a metal. </li></ul></ul><ul><ul><li>Nonmetallic. </li></ul></ul><ul><ul><ul><li>Vitreous (glassy). </li></ul></ul></ul><ul><ul><ul><li>Satiny. </li></ul></ul></ul><ul><ul><ul><li>Silky. </li></ul></ul></ul><ul><ul><ul><li>Resinous. </li></ul></ul></ul><ul><ul><ul><li>Pearly. </li></ul></ul></ul><ul><ul><ul><li>Earthy (dull). </li></ul></ul></ul><ul><ul><ul><li>Adamantine (brilliant). </li></ul></ul></ul>Satin spar Gypsum – Satiny luster Quartz – Vitreous luster
  22. 22. <ul><li>Scratching resistance of a mineral. </li></ul><ul><li>Hardness compared to the Mohs hardness scale. </li></ul><ul><ul><li>Talc, Graphite. </li></ul></ul><ul><ul><li>Gypsum. </li></ul></ul><ul><ul><li>Calcite. </li></ul></ul><ul><ul><li>Fluorite. </li></ul></ul><ul><ul><li>Apatite. </li></ul></ul><ul><ul><li>Orthoclase. </li></ul></ul><ul><ul><li>Quartz. </li></ul></ul><ul><ul><li>Topaz. </li></ul></ul><ul><ul><li>Corundum. </li></ul></ul><ul><ul><li>Diamond. </li></ul></ul>Hardness Glass - Steel 5.5 Fingernail 2.5 Copper Penny 3.5 Steel File 6.5
  23. 23. Specific Gravity <ul><li>Related to density (mass per volume) </li></ul><ul><li>Mineral weight over weight of equal water volume. </li></ul><ul><li>Specific gravity is “heft”– How heavy it feels. </li></ul><ul><ul><li>Pyrite – Heavy (SG 5.0) </li></ul></ul><ul><ul><li>Feldspar – Light (SG 2.6) </li></ul></ul><ul><li>Pyrite “feels” heavier than feldspar. </li></ul>Pyrite Potassium Feldspar
  24. 24. Crystal Habit <ul><li>Crystal habit is the ideal shape of crystal faces. </li></ul><ul><li>Ideal faces require ideal growth conditions. </li></ul><ul><li>Many descriptive terms are used to characterize habit. </li></ul>Cubes Hexagonal Prisms Blades Rhombohedra Dodecahedra Octahedra Tetragonal Prisms Compound Forms
  25. 25. Crystal Form <ul><li>Minerals vary in crystal face development. </li></ul><ul><ul><li>Euhedral – Good crystal faces; grown in open cavity. </li></ul></ul><ul><ul><li>Anhedral – No crystal faces; grown in tight space. </li></ul></ul><ul><ul><li>Subhedral – Between the two. </li></ul></ul><ul><li>Face development indicates growth history. </li></ul><ul><li>Anhedral crystals common; euhedral less so. </li></ul>Amethyst Geode
  26. 26. Cleavage <ul><li>Tendency to break along planes of lattice weakness. </li></ul><ul><li>Cleavage produces flat, shiny surfaces. </li></ul><ul><li>Described by the number of planes and their angles. </li></ul><ul><li>Sometimes mistaken for crystal habit. </li></ul><ul><ul><li>Cleavage is through going; often forms parallel “steps”. </li></ul></ul><ul><ul><li>Habit is only on external faces. </li></ul></ul><ul><li>1, 2, 3, 4, and 6 cleavages possible. </li></ul>
  27. 27. Cleavage <ul><li>Examples of Cleavage: </li></ul><ul><ul><li>1 direction </li></ul></ul><ul><ul><li>2 directions at ~ 90º </li></ul></ul><ul><ul><li>2 directions NOT at 90º </li></ul></ul>Muscovite Mica Potassium Feldspar Amphibole
  28. 28. Cleavage <ul><li>Examples of Cleavage: </li></ul><ul><ul><li>Three directions at 90º </li></ul></ul><ul><ul><li>Three directions NOT at 90º </li></ul></ul>Halite Calcite
  29. 29. Fracture <ul><li>Some minerals lack planes of lattice weakness. </li></ul><ul><li>Due to equal molecular bonds in all directions. </li></ul><ul><li>These minerals don’t cleave; they exhibit fracture. </li></ul><ul><ul><li>Example: Quartz displays conchoidal fracture. </li></ul></ul><ul><ul><ul><li>Shaped like the inside of a clam shell. </li></ul></ul></ul><ul><ul><ul><li>Breaks along smooth, curved surfaces. </li></ul></ul></ul><ul><ul><ul><li>Produces extremely sharp edges. </li></ul></ul></ul>Obsidian
  30. 30. Mineral Compositions <ul><li>Only about 50 minerals are abundant. </li></ul><ul><li>98% of crustal mineral mass is from eight elements. </li></ul><ul><ul><li>Oxygen O 46.6% </li></ul></ul><ul><ul><li>Silicon Si 27.7% </li></ul></ul><ul><ul><li>Aluminum Al 8.1% </li></ul></ul><ul><ul><li>Iron Fe 5.0% </li></ul></ul><ul><ul><li>Calcium Ca 3.6% </li></ul></ul><ul><ul><li>Sodium Na 2.8% </li></ul></ul><ul><ul><li>Potassium K 2.6% </li></ul></ul><ul><ul><li>Magnesium Mg 2.1% </li></ul></ul><ul><ul><li>All others 1.5% </li></ul></ul>74.3% of crustal minerals !!!
  31. 31. Mineral Classes <ul><li>Minerals are classified based upon the dominant anion. </li></ul><ul><ul><li>Silicates SiO 2 4- Rock-forming minerals </li></ul></ul><ul><ul><li>Oxides O 2- Magnetite, Hematite </li></ul></ul><ul><ul><li>Sulfides S - Pyrite, Galena </li></ul></ul><ul><ul><li>Sulfates SO 4 2- Gypsum </li></ul></ul><ul><ul><li>Halides Cl - or F - Fluorite, Halite </li></ul></ul><ul><ul><li>Carbonates CO 3 2- Calcite, Dolomite </li></ul></ul><ul><ul><li>Native elements Cu, Au, C Copper, Gold, Graphite </li></ul></ul>Fluorite (Halide) Native Copper Malachite (Carbonate)
  32. 32. Silicate Minerals <ul><li>Silicates are know as “the rock-forming minerals.” </li></ul><ul><li>They dominate Earth’s crust. </li></ul><ul><ul><li>Oxygen and silicon… </li></ul></ul><ul><ul><ul><li>Make up 94.7% of crustal volume, and... </li></ul></ul></ul><ul><ul><ul><li>74.3% of crustal mass. </li></ul></ul></ul>
  33. 33. Silicate Minerals <ul><li>The anionic unit is the silica tetrahedron. </li></ul><ul><ul><li>4 oxygen atoms are bonded to 1 silicon atom (SiO 4 4- ). </li></ul></ul><ul><ul><li>Silicon is tiny; oxygen is huge. </li></ul></ul><ul><ul><li>The silica tetrahedron has a net -4 ionic charge. </li></ul></ul><ul><ul><li>The silicate unit can be depicted by… </li></ul></ul><ul><ul><ul><li>Spheres. </li></ul></ul></ul><ul><ul><ul><li>A ball-and-stick model. </li></ul></ul></ul><ul><ul><ul><li>Polyhedra. </li></ul></ul></ul>
  34. 34. Silicate Minerals <ul><li>Silica tetrahedra link together by sharing oxygens. </li></ul><ul><li>More shared oxygen = lower Si:O ratio; governs… </li></ul><ul><ul><li>Melting temperature. </li></ul></ul><ul><ul><li>Mineral structure and cations present. </li></ul></ul><ul><ul><li>Susceptibility to chemical weathering. </li></ul></ul>Type of Silicate Structure Formula Si:O Ratio Independent Tetrahedra SiO 4 0.25 Double Tetrahedra Si 2 O 7 0.29 Ring Silicates Si 6 O 18 0.33 Single Chains SiO 3 0.33 Double Chains Si 4 O 11 0.36 Sheet Silicates Si 2 O 5 0.40 Framework Silicates SiO 2 0.50
  35. 35. Independent Tetrahedra <ul><li>Tetrahedra share no oxygens–they are linked by cations. </li></ul><ul><ul><li>Olivine group. </li></ul></ul><ul><ul><ul><li>High-temperature Fe-Mg silicate. </li></ul></ul></ul><ul><ul><ul><li>Small green crystals; no cleavage. </li></ul></ul></ul><ul><ul><li>Garnet group. </li></ul></ul><ul><ul><ul><li>Equant crystals with no cleavage. </li></ul></ul></ul><ul><ul><ul><li>Dodecahedral (12-sided) crystals. </li></ul></ul></ul>Kyanite Garnet
  36. 36. Single-Chain Silicates <ul><li>Single-chain structures bonded with Fe and Mg. </li></ul><ul><ul><li>Pyroxene Group. </li></ul></ul><ul><ul><ul><li>Black-to-green color. </li></ul></ul></ul><ul><ul><ul><li>Two distinctive cleavages at nearly 90°. </li></ul></ul></ul><ul><ul><ul><li>Stubby crystals. </li></ul></ul></ul><ul><ul><ul><li>Augite is the most common pyroxene. </li></ul></ul></ul>Pyroxene
  37. 37. Double-Chain Silicates <ul><li>Double chain of silica tetrahedra bonded together. </li></ul><ul><li>Contain a variety of cations. </li></ul><ul><ul><li>Amphibole group - two perfect cleavages; </li></ul></ul><ul><ul><li>elongate crystals. </li></ul></ul>Hornblende
  38. 38. Sheet Silicates <ul><li>Two dimensional sheets of linked tetrahedra. </li></ul><ul><li>Characterized by one direction of perfect cleavage. </li></ul><ul><ul><li>Mica group – Biotite (dark) and Mucsovite (light). </li></ul></ul><ul><ul><li>Clay mineral group – Feldspar-weathering residue; tiny. </li></ul></ul>Muscovite Mica
  39. 39. Framework Silicates <ul><li>All four oxygens in the silica tetrahedra are shared. </li></ul><ul><ul><li>Feldspar group – Plagioclase and potassium feldspar. </li></ul></ul><ul><ul><li>Silica (Quartz) group – Contains only Si and O. </li></ul></ul>Potassium Feldspar
  40. 40. Gems <ul><li>Minerals with special value. </li></ul><ul><ul><li>Rarity. </li></ul></ul><ul><ul><li>Beauty. </li></ul></ul><ul><ul><ul><li>Color. </li></ul></ul></ul><ul><ul><ul><li>Interaction with light. </li></ul></ul></ul><ul><ul><ul><ul><li>Dispersion. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>High refractive index. </li></ul></ul></ul></ul>Watermelon Tourmaline Aquamarine Beryl
  41. 41. Gems <ul><li>Gems are cut and polished to be used in jewelry. </li></ul><ul><ul><li>Facets are ground onto a gemstone by a machine. </li></ul></ul><ul><ul><li>Facets are not natural crystal faces. </li></ul></ul>
  42. 42. Diamonds <ul><li>Diamonds originate under extremely high pressure. </li></ul><ul><ul><li>~ 150 km deep (upper mantle). </li></ul></ul><ul><ul><li>Pure carbon is compressed into the diamond structure. </li></ul></ul><ul><li>Rifting causes deep mantle rock to move upward. </li></ul><ul><li>Diamonds are found in kimberlite pipes. </li></ul>
  43. 43. W. W. Norton & Company Independent and Employee-Owned <ul><li>This concludes the Norton Media Library PowerPoint Slide Set for Chapter 3 </li></ul><ul><li>Essentials of Geology </li></ul><ul><li>3 rd Edition (2009) </li></ul><ul><li>by Stephen Marshak </li></ul>