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Chapter 14

Chapter 14. Classification and names of minerals. Mineral varieties: isomorphism. Garnets Same crystal system and morphology Considerable difference in chemical composition and with that density, hardness, refractive index and unit cell parameters differ

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Chapter 14

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  1. Chapter 14 Classification and names of minerals

  2. Mineral varieties: isomorphism • Garnets • Same crystal system and morphology • Considerable difference in chemical composition and with that density, hardness, refractive index and unit cell parameters differ • Plot compositions between 3 end members in pyralspyte garnet series (Fe, Mg, Mn-rich) on ternary diagram • Composition in reality range between these components and general formula is (Fe, Mg, Mn)3Al2(SiO4)3 • The relative ratios of Fe, Mg, Mn differ for the different garnets: pyrope, spessartite, almandite • Uvarovite series garnets have the endmembers: andradite, grossular, ugrandite • Carbonates • Calcite, magnesite, rhodochrosite, siderite • Compositions vary but same morphology • Most carbonates rather close to end-member compositions • Carbonates with intermediate compositions has different morphology than above minerals

  3. Mineral varieties: polymorphism • Different mineral species: different morphology but same chemical compositions • SiO2 minerals (silica minerals): quartz trigonal stishovite tetragonal tridymite hexagonal etc.

  4. Elementary chemical composition • 4000 mineral species with individual mineral names (currently) • Within species different polytypes: • Quartz: amethyst, citrine, rosequartz, etc.; • Beryl: emerald (Cr-rich); aquamarine (Fe-rich) • Common minerals contain abundant elements: O, H, Si, Al, Na, Mg, Ca, Fe, K • Lithofile, chalcofile, siderofile, halogenofile, atmofile

  5. Silicates

  6. Classification of minerals • Genetic: • According to principal processes by which minerals are formed • Not mineralogical and problematic • Geochemical • Based on principal chemical elements • Irrational: minerals that consist of many elements? • Crystal chemical • Functional relationship between chemical composition • Acceptable • Geochemical and crystal chemical • Very useful

  7. Classification

  8. Chapter 15 Mineral identification of hand specimens Self study and watch video on Blackboard: Identification of minerals

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