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Chapter 3: Matter and Minerals (part II)

Chapter 3: Matter and Minerals (part II). Minerals: the building blocks of rocks. Definition of a Mineral: naturally occurring inorganic solid characteristic crystalline structure definite chemical composition. How do we identify minerals?. Physical properties: Color Luster

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Chapter 3: Matter and Minerals (part II)

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  1. Chapter 3: Matter and Minerals (part II)

  2. Minerals: the building blocks of rocks • Definition of a Mineral: • naturally occurring • inorganic • solid • characteristic crystalline structure • definite chemical composition

  3. How do we identify minerals? • Physical properties: • Color • Luster • Hardness • Crystal shape • Cleavage • Specific gravity • Other

  4. Physical Properties of Minerals • Color: • Most obvious, but often misleading • Different colors may result from impurities Example: Quartz

  5. Physical Properties of Minerals • Color: Streak – color of a mineral in powdered form (used for metallic minerals) Obtained by scratching a mineral on a piece of unglazed porcelain. Example: Hematite

  6. Physical Properties of Minerals • Luster: • How a mineral surface reflects light • Two major types: • Metallic luster • Non-metallic luster Metallic example: Galena Non-metallic example: Orthoclase

  7. Physical Properties of Minerals • Hardness: • How easy it is to scratch a mineral • Mohs Scale of Hardness • relative scale • consists of 10 minerals, ranked 1 (softest) to 10 (hardest)

  8. Hardest (10) – Diamond Softest (1) – Talc Common objects: - Fingernail (2.5) - Copper penny (3.5) - Wire nail (4.5) - Glass (5.5) - Streak plate (6.5) Mohs Scale of Hardness

  9. Physical Properties of Minerals • Crystal shape (or form): • external expression of a mineral’s internal atomic structure • planar surfaces are called crystal faces • angles between crystal faces are constant for any particular mineral Pyrite Quartz

  10. Physical Properties of Minerals • Cleavage vs. Fracture: • The way a mineral breaks • Cleavage: tendency of a mineral to break along planes of weakness • Minerals that do not exhibit cleavage are said to fracture • Do not confuse cleavage planes with crystal faces! Crystal faces are just on the surface and may not repeat when the mineral is broken.

  11. Physical Properties of Minerals • Cleavage is described by: • Number of planes • Angles between adjacent planes • These are constant for a particular mineral

  12. Physical Properties of Minerals • Cleavage (1 direction): Example: mica

  13. Physical Properties of Minerals • Cleavage (2 directions): orthoclase amphibole

  14. Physical Properties of Minerals • Cleavage (3 directions): halite calcite

  15. Physical Properties of Minerals • Cleavage (4 directions): fluorite

  16. Physical Properties of Minerals • Fracture: • minerals that do not exhibit cleavage are said to fracture • smooth, curved surfaces when minerals break in a glass-like manner: conchoidal fracture Quartz

  17. Physical Properties of Minerals • Specific gravity: • weight of a mineral divided by weight of an equal volume of water • metallic minerals tend to have higher specific gravity than non-metallic minerals Galena SG=7.5 Quartz SG=2.67

  18. Physical Properties of Minerals • Other properties: • reaction with hydrochloric acid(calcite fizzes) • taste(halite tastes salty) • feel(talc feels soapy, graphite feels greasy) • magnetism(magnetite attracts a magnet)

  19. Mineral Groups • Rock-forming minerals • ~30 common minerals make up most rocks in Earth’s crust • Composed mainly of the 8 elements that make up over 98% of the crust

  20. Mineral Groups Element Abundances Silica (SiO4)4- SILICATES Common cations that bond with silica anions All others: 1.5%

  21. Mineral Groups • Silicates (most abundant) • Non-silicates (~8% of Earth’s crust): • Oxides O2- • Carbonates (CO3)2- • Sulfides S2- • Sulfates (SO4)2- • Halides Cl-, F-, Br- • Native elements (single elements; e.g., Au)

  22. Mineral Groups – Silicates Silicon-oxygen tetrahedron (SiO4)4- • Silicates • Tetrahedron • fundamental building block • 4 oxygen ions surrounding a much smaller silicon ion

  23. Mineral Groups – Silicates • Joining Silicate Structures • How tetrahedra may be linked: • independent tetrahedra • single chains • double chains • sheets • 3-D framework

  24. Mineral Groups– Silicates –

  25. Mineral Groups – Silicates Olivine Group dark silicates (Fe-Mg)  ferromagnesian No cleavage

  26. Mineral Groups – Silicates Pyroxene Group Ferromagnesian / dark silicates (Fe-Mg) Augite 2-directions of cleavage (at nearly 90 degrees)

  27. Mineral Groups – Silicates Amphibole Group Ferromagnesian / dark silicates (Ca, Fe-Mg) Hornblende 2-directions of cleavage (not at 90 degrees)

  28. Mineral Groups – Silicates Mica Group and Clay Minerals light silicates (K, Al)  non-ferromagnesian Muscovite 1-direction of cleavage

  29. Mineral Groups – Silicates Feldspar Group light silicates (K-Na-Ca, Al) K-feldspar Most common mineral group Orthoclase Plagioclase 2-directions of cleavage (at 90 degrees) Ca/Na-feldspar

  30. Mineral Groups – Silicates Quartz light silicates (pure SiO2) no cleavage (conchoidal fracture) hard, resistant to weathering Quartz

  31. Mineral Groups Non-ferromagnesian Silicates (K, Na, Ca, Al) Ferromagnesian Silicates (Fe, Mg) Oxides Carbonates Sulfides/sulfates Native elements

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