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Minerals

Minerals. Chapter 3. Minerals known to ancient peoples. Crystalline Structure. Chemistry within limits Internal Structure within limits Permits identification based on chemical and physical properties. Minerals are orderly crystalline structures. Helium Atomic Number 2 Atomic Weight 4.

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Minerals

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  1. Minerals Chapter 3

  2. Minerals known to ancient peoples

  3. Crystalline Structure • Chemistry within limits • Internal Structure within limits • Permits identification based on chemical and physical properties

  4. Minerals are orderly crystalline structures

  5. Helium Atomic Number 2 Atomic Weight 4 Neon Atomic Number 10 Atomic Weight 20

  6. Atoms Same number of protons and electrons No charge Inert Ions Gain or loose electrons to fill outer electron shell Charged Larger or smaller than atom Atoms and Ions

  7. Anion Gains electrons Negative charge Larger that atom Cation Loose electrons Positive charge Smaller than atom Metals Ions

  8. 8 most abundant elements in the Earth’s crust • Element Symbol Charge Size Atom Size Ion • Oxygen O - - 0.60 1.40 • Silicon Si ++++ 1.17 0.42 • Aluminum Al +++ 1.43 0.51 • Iron Fe ++ (+++) 1.24 0.74 • Calcium Ca ++ 1.96 0.99 • Sodium Na + 1.86 0.97 • Potassium K + 2.31 1.33 • Magnesium Mg ++ 1.60 0.66

  9. Organization of ions into a crystal lattice • Sizes of ions • Charges of ions • Unit Cell is the smallest assemblage of ions that satisfies both ionic sizes and charges • The unit cell is much larger the simple chemical formula

  10. Coordination • Radius Ratio Coordination Number 1.000 12 0.999 - 0.732 8 0.731 – 0.414 6 0.413 – 0.225 4 0.224 – 0.115 3 <0.114 2

  11. Coordination • Coordination is controlled by the relative sizes of ions • Radius ratio is Radius of Cation divided by Radius of Anion • Limits 0.01 and 1.00

  12. Example • Na cation 0.97 • Cl anion 1.81 • Radius Ratio 0.54 • Coordination Number 6 • Can fit 6 sodium ions around a chlorine ion • Conversely there are 6 chlorine ions around a sodium ion

  13. Common Salt (NaCl)6 Cl ions around each Na ion

  14. Next balance the charges • 6 Na at -1 = -6 • 6 Cl at +1 = +6 • Net charge = 0

  15. Oxygen and Silicon • O ionic radius 1.40 -2 • Si ionic radius 0.42 +4 • Radius Ratio 0.3 • Coordination Number 4 • 4 O -2 = -8 • 1 Si +4 = +4 • Net Charge -4

  16. Silicate Tetrahedron (-4)

  17. Silicate Tetrahedron • Stick Model Cell Model Schematic

  18. Mineral Classes(Simple) • Elements (12 fold coordination) • Oxides (4 and 6 fold coordination) • Sulfides (6 fold coordination) • Halides (6 fold coordination)

  19. Halite -- Pyrite -- Galena

  20. Mineral ClassesCompound • Carbonates (CO3) -2 2.95 3 fold • Sulfates (SO4) -2 3.08 3 fold • Silicates (SiO4 ) -4 3.20 4 fold

  21. Silicates Island (olivine)

  22. Island Silicate

  23. Single ChainPyroxene

  24. Double ChainAmphibole

  25. Sheet (mica)

  26. Framework Feldspar

  27. Unit Cell • Controls crystal form • Controls cleavage • Controls fracture • Revealed by striations on crystal and cleavage faces

  28. Crystallization from melt (Plutonists) • Igenous • Precipitation from water (Neptunists) • Sediment • Transformation of organic materials • Sediment • Chemical transformation from previous minerals • metamorphism

  29. Assignment • Chapter 4 Igneous Rocks • Important terms • Magma • Texture • Bowen’s reaction series • Crystallization – Melting

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