2.6 Systematic Mineralogy

2.6 Systematic Mineralogy - Systematic Mineralogy Mineral...

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Unformatted text preview: Systematic Mineralogy Mineral classification schemes: True classification relies on both: Crystal chemistry (crystallography) Chemical composition (simplest) Chemical classification based on anions Chemistry easy to determine Xray diffraction (early 20th century) required for structures Single anion (Cl) Anion group (SiO44) Mineral group Native elements Oxides Hydroxides Halides Sulfides Sulfates Carbonates Phosphates Silicates Anion or anion gp N/A O2 OH Cl, Br, F S2 SO42 CO32 PO43 SiO44 Divisions Class (anion division) Family (structural division) Group (structural division) Series (solid solution) Species (individual minerals) Varieties (substituted elements) Example Cagrunerite: A Carich variety Of a mineral species In the cummingtonitegrunerite series Of the amphibole group Of the inosilicate family Of the silicate class Silicates The most common group of minerals forming Earth's crust 25% of all minerals (~1000) 40% of rock forming minerals 90% of earth's crust i.e those minerals you are likely to find Valuable Gems Soils Industrial minerals Geologic history/processes Silicate Structure Basic building block: silica tetrahedron Si4+ with four O2 surrounding it Net charge is 4 Mesodesmic, polymerization Tetrahedron can share oxygen atoms Silica Tetrahedron Fig. 111 Six groups of silicate minerals Orthosilicates = Nesosilicates Disilicates = Sorosilicates Single tetrahedron Ring silicates = Cyclosilicates Two tetrahedrons share single oxygen 4, 5, or 6 tetrahedron share two oxygen Chain silicates = Inosilicates Sheet silicates = Phyllosilicates 2 or 3 oxygen shared, arranged in single or double chain 3 oxygen shared in sheets All 4 oxygen are shared Framework silicates = Tectosilicates Ortho Di Ring Chain double and single Sheet Tecto Fig. 112 Z/O ratios Z = Si tetrahedral sites Z/O ratio depends on type of silicate Can be other cations, most commonly Al Ortho = 1/4 Di = 2/7 Ring = 1/3 Chain , single = 1/3; double = 4/11 Sheet = 2/5 Framework = 1/2 Other parts of Silicates Quartz (and polymorphs) only minerals with only Si and O All other silicates are charge balanced by other cations "glue" that holds together silica tetrahedron Degree of polymerization depends on availability of Si Quartz and feldspars (framework): Sirich environments Olivine (orthosilicate): Sipoor environment Si/O = Si/O = Mafic vs Felsic Mafic rich in Magnesium and Iron (Ferrum), Sipoor Felsic rich in Si and Al E.g. biotite, amphiboles, pyroxenes, and olivine Commonly dark colored E.g. Feldspars, Quartz (SiO2), muscovite, feldspathoids Commonly light colored ...
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