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06 minerals rocks_forstudents

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06 minerals rocks_forstudents

  1. 1. Minerals and Rocks Chapter 5
  2. 2. Outline• Minerals and rocks -What are minerals? Geologic definition, significance. -What are rocks? Geologic definition, 3 main types.• Mineral structure -Crystalline structure, crystals, crystal lattice -Determining atom arrangement (XRD), atomic bonding -Polymorphs, crystal growth and packing of atoms• Physical properties of minerals -Overview: common ones, less common ones -Color, streak, luster, hardness, specific gravity, crystal habit/form, fracture, and cleavage• Mineral classes and silicates -Mineral classes, most importantly silicates -Silica tetrahedra building block -Silicate types: from individual tetrahedra to framework Chapter 5 5 Chapter
  3. 3. Minerals• The “building blocks” of rocks, and hence, of Earth.• -more than 4000 are known• -dozens of new minerals are discovered annually• Chapter 5
  4. 4. Minerals• Societies depend on mineral resources.• Metals: iron, copper, lead, zinc, nickel, aluminum, etc.• Non-metals: gypsum, limestone, clay Chapter 5
  5. 5. Minerals• Economically important – Drive world economies.• Historically important – Dictated human history. • Iron. • Copper. • Gold. • Diamonds. • Gems. Chapter 5
  6. 6. Mineral Definition• Geologic definition of a mineral is specific.• A naturally occuring solid, formed geologically, that has a crystal structure and a specific chemical composition, and is usually inorganic• -doesn’t include “minerals in nutritional sense• -A mineraloid exhibits some, but not all, properties Gypsum Chapter 5
  7. 7. Rocks• Rocks are Earth materials made from minerals.• Most rocks have more than one kind of mineral.• -example: granite• -mineral(s)?• Potassium, quartz, hornblende• -some are mono-mineralic• Limestone (calcite), rock salt• (halite), glacial ice Chapter 5
  8. 8. Rock Definition• Geologists definition: coherent, naturally occuring solid made up of an aggregate of minerals (or more Chapter 5
  9. 9. 3 Main Rock Types1. Igneous – solidified from molten rock or melt Chapter 5
  10. 10. 3 Main Rock Types2. Sedimentary3. -cemented/precipitated from rock fragments/solution Chapter 5
  11. 11. 3 Main Rock Types3. Metamorphic – existing rock altered by changes in pressure and temperature Chapter 5
  12. 12. Outline• Minerals and rocks -What are minerals? Geologic definition, significance. -What are rocks? Geologic definition, 3 main types.• Mineral structure -Crystalline structure, crystals, crystal lattice -Determining atom arrangement (XRD), atomic bonding -Polymorphs, crystal growth and packing of atoms• Physical properties of minerals -Overview: common ones, less common ones -Color, streak, luster, hardness, specific gravity, crystal habit/form, fracture, and cleavage• Mineral classes and silicates -Mineral classes, most importantly silicates -Silica tetrahedra building block -Silicate types: from individual tetrahedra to framework Chapter 5 5 Chapter
  13. 13. Crystalline Structure• A solid with disordered atoms is called a glass Glass• Atoms in a mineral are specifically ordered• Crystalline structure based on atomic patterns Chapter 5
  14. 14. Crystals• Minerals displaying flat external faces (rare).• -crystal faces form best in open cavities• -crystals are often prized mineral specimens Beryl Quartz Green, gem version -> emerald Chapter 5
  15. 15. Crystals• Constancy of angles between crystal faces.• -same mineral always (ideal) has same crystal faces• -adjacent faces occur at regular (diagnostic) angle• Faces and angles reflect the atomic arrangement. Chapter 5
  16. 16. Crystal Lattice• Ordered atoms in crystals form a lattice.• Lattices are patterns that repeat in 3D• This internal pattern controls mineral properties.• -crystal shape• -planes of symmetry • Chapter 5
  17. 17. Determining Atom Arrangements• X-Ray Diffraction (XRD) probes crystal lattices.• Unique lattice spacing is used to ID minerals. Chapter 5
  18. 18. Bonding of Atoms• Lattice atoms are held in place by atomic bonds.  Bond characteristics govern mineral properties.• 5 recognized types of bonds (Appendix A).• -covalent (gain/loose )• -metallic• -van Chapter 5
  19. 19. Polymorphs (many + form)• Same composition but different crystal structure.• Polymorphs show the importance of bond type.• Diamond and graphite are carbon polymorphs (C)• -diamond: strong covalent bonds; hardest mineral• -graphite: weak van der waals bonds; softest mineral Diamond Graphite Chapter 5
  20. 20. Crystal Growth• Crystals grow as atoms attach to mineral surfaces• -growth starts from a central seed crystal• -growth expands outward Chapter 5
  21. 21. Crystal Growth• Outward crystal growth fills available space.• Resulting crystal shape governed by surroundings.• -open space: good crystal faces grow• -confined space: no crystal spaces• Crystals mostly grow by…• Solidification from a melt• Precipitation from solution Chapter 5
  22. 22. Atomic Packing• Ion size (radius) and charge control packing. • Ion – atom charged due to gain or loss of an electron • Cation – positive ion due to loss of electron • Anion – negative ion due to gain of electron• Ionic radii due to # of electrons; anions are bigger. Chapter 5
  23. 23. Atomic Packing• Anions and cations bond to neutralize charges.• Anion – Cation “fit” governed by relative size.• -large central cation – larger number of anions• -smalll central cation – smaller number of anions Chapter 5
  24. 24. Outline• Minerals and rocks -What are minerals? Geologic definition, significance. -What are rocks? Geologic definition, 3 main types.• Mineral structure -Crystalline structure, crystals, crystal lattice -Determining atom arrangement (XRD), atomic bonding -Polymorphs, crystal growth and packing of atoms• Physical properties of minerals -Overview: common ones, less common ones -Color, streak, luster, hardness, specific gravity, crystal habit/form, fracture, and cleavage• Mineral classes and silicates -Mineral classes, most importantly silicates -Silica tetrahedra building block -Silicate types: from individual tetrahedra to framework Chapter 5 5 Chapter
  25. 25. Physical Properties of Minerals• Characteristics determined by your senses.• Used to ID minerals.• Properties depend upon…• -chemical composition• -crystal structureSome are diagnostic.i.e. pyrite (fes2) Pyrite-minerals have a unique Chapter 5
  26. 26. Physical Properties• Common properties: • Color. • Streak. • Luster. • Hardness. • Specific gravity. • Crystal habit (ideal shape). • Crystal form. • Fracture. • Cleavage. Needle-like crystal habit Chapter 5
  27. 27. Physical Properties• Less common physical properties: • Taste. Magnetite crystals on a large magnet. • Smell. • Feel. • Magnetism. • Effervescence. • Refractive index. • Malleability. Calcite effervesces with acid Chapter 5
  28. 28. Color• Color is diagnostic for some minerals.• E.g. olivine/malachite is always green, azurite is always blueSome minerals may exhibit a broad color range.-quartz (clear, white, yellow, pink, purple Quartz – Many colors Malachite – always green Chapter 5
  29. 29. Streak• Color of a mineral struck across unglazed porcelain.• Streak is often a useful diagnostic property. • Congruent streak –streak color same as mineral • -magnetite: black mineral; black streak Incongruent streak – streak color different than mineral -chromite: black mineral; greenish-brown streak Hematite – Red-brown streak Chapter 5
  30. 30. Luster• The way a mineral scatters light.• Two subdivisions. • Metallic – Looks like a metal. • Nonmetallic. • Vitreous (glassy). • Satiny. • Silky. • Resinous. • Pearly. Quartz – Vitreous luster • Earthy (dull). • Adamantine (brilliant). Satin spar Gypsum – Satiny luster Chapter 5
  31. 31. Hardness• Scratching resistance of a mineral.• Hardness compared to Mohs Hardness Scale. 1. Talc, Graphite 2. Gypsum Fingernail 2.5 3. Calcite Copper Penny 3.5 4. Fluorite 5. Apatite Glass - Steel 5.5 6. Orthoclase Steel File 6.5 7. Quartz 8. Topaz 9. Corundum 10. Diamond Chapter 5
  32. 32. Specific Gravity• Related to density (mass per volume).• Mineral weight over weight of equal water volume.• Specific gravity is heft – how heavy it feels• -pyrite: heavy (sg 5.0)• -feldspar: light (sg 2.6)• -pyrite feels heavier Pyrite Potassium Feldspar Chapter 5
  33. 33. Crystal Habit• Crystal habit is the ideal shape of crystal faces.• -ideal growth requires ideal conditions• -many terms are used to describe habit Cubes Octahedra Blades Hexagonal Prisms Dodecahedra Rhombohedra Tetragonal Prisms Chapter 5
  34. 34. Crystal Form• Minerals vary in crystal face development. • Euhedral – good crystal faces; gown in open cavity • Anhedral – no crystal faces; grown in tight space • Subhedral – between the two• Face development indicates growth history• Anhedral crystals common; euhedral less so. Amethyst Geode Chapter 5
  35. 35. Fracture• Some minerals lack planes of weakness. • Due to equal molecular bonds in all directions. • These minerals fracture and hence don’t have cleavage. • Example: Quartz Obsidian Chapter 5
  36. 36. Cleavage• Tendency to break along planes of weakness.• Due to equal molecular bonds in all directions.• These minerals fracture and hence don’t have cleavage.• i.e. quartz displays conchoidal fracture• -shaped like inside of a clam shell• -breaks along smooth curved surfaces• -cleavage produces flat surfaces• -described by number of planes and their angles• Sometimes mistaken for crystal habit. Chapter 5
  37. 37. Cleavage• Examples of Cleavage: Muscovite Mica • 1 direction • 2 directions at 90º Potassium Feldspar • 2 directions NOT at 90º Amphibole Chapter 5
  38. 38. Outline• Minerals and rocks -What are minerals? Geologic definition, significance. -What are rocks? Geologic definition, 3 main types.• Mineral structure -Crystalline structure, crystals, crystal lattice -Determining atom arrangement (XRD), atomic bonding -Polymorphs, crystal growth and packing of atoms• Physical properties of minerals -Overview: common ones, less common ones -Color, streak, luster, hardness, specific gravity, crystal habit/form, fracture, and cleavage• Mineral classes and silicates -Mineral classes, most importantly silicates -Silica tetrahedra building block -Silicate types: from individual tetrahedra to framework Chapter 5 5 Chapter
  39. 39. Mineral Classes• Minerals are classified by their dominant anion. Silicates SiO24- Most rock-forming mins! • Oxides O2- Magnetite, Hematite • Sulfides S- Pyrite, Galena • Sulfates SO42- Gypsum • Halides Cl- or F- Fluorite, Halite • Carbonates CO32- Calcite, Dolomite • Native Elements Cu, Au, C Copper, Gold, GraphiteMalachite (Carbonate) Fluorite (Halide) Native Copper Chapter 5
  40. 40. Silicate Minerals• Silicates are known as the rock-forming minerals.• They dominate the Earth’s crust.• Oxygen and silicon…• -94.7% of crustal volume• -74.3% of crustal mass Chapter 5
  41. 41. Silicate Minerals• The building block (anion) unit is the silica tetrahedron. • 4 oxygen atoms are bonded to 1 silicon atom (SiO44-). • -silicon is tiny; oxygen is huge • -the silica tetrahedron has a net -4 ionic charge • -the silicate unit can be depicted by… • -spheres • -ball and stick model • -polyhedra Chapter 5
  42. 42. Silicate Minerals• Silica tetrahedra link together by sharing oxygens.• More shared oxygen  higher Si:O ratio; governs…• -melting temp• -mineral structure and cations present• -susceptibility to chemical weathering Type of Silicate Structure Formula Si:O Ratio Independent Tetrahedra SiO4 0.25 Double Tetrahedra Si2O7 0.29 Ring Silicates Si6O18 0.33 Single Chains SiO3 0.33 Double Chains Si4O11 0.36 Sheet Silicates Si2O5 0.40 Framework Silicates SiO2 0.50 Chapter 5
  43. 43. Independent Tetrahedra• Tetrahedra share no oxygens - linked by cations. • Olivine Group. • High temperature Fe-Mg silicate. • Small green crystals; no cleavage. • Garnet Group. • Equant crystals with no cleavage. • Dodecahedral (12 sided) crystals.Garnet Chapter 5
  44. 44. Single-Chain Silicates• Single-chain structures bonded with Fe and Mg. • Pyroxene Group. • Black to green color. • Two distinctive cleavages at nearly 90°. • Stubby crystals. • Augite is the most common pyroxene. Pyroxene Chapter 5
  45. 45. Double-Chain Silicates• Double chain of silica tetrahedra bonded together.• Contain a variety of cations. • Amphiboles – two perfect cleavages • Elongate crystalsHornblende Chapter 5
  46. 46. Sheet Silicates• 2-dimensional sheets of linked tetrahedra.• Characterized by one direction of perfect cleavage. • Mica Group – botite (dark) and mucsovite (light) Clay Mineral Group – feldspar weathering residue; tiny Muscovite (Mica) Chapter 5
  47. 47. Framework Silicates• All 4 oxygens in the silica tetrahedra are shared. • Feldspar Group – plagioclase and potassium feldspar • Silica (Quartz) Group – contains only si and o Potassium Feldspar Chapter 5

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