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Systematic Mineralogy

Systematic Mineralogy. Description of how minerals are divided into groups Groups based on anions Single anion ( Cl - ) Anion group (SiO 4 4- ) Further divided based on structures. Divisions. Class (anion division) Family (structural division – silicates mostly)

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Systematic Mineralogy

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  1. Systematic Mineralogy • Description of how minerals are divided into groups • Groups based on anions • Single anion (Cl-) • Anion group (SiO44-) • Further divided based on structures

  2. Divisions • Class (anion division) • Family (structural division – silicates mostly) • Group (structural division) • Series (solid solution) • Species (individual minerals) • Varieties (substituted elements)

  3. Example • Ca-grunerite: • A Ca-rich variety • Of a mineral species • In the cummingtonite-gruneriteseries • Of the amphibole group • Of the inosilicatefamily • Of the silicate class

  4. 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

  5. Silicate Structure • Basic building block: silica tetrahedron • Si4+ with four O2- surrounding it • Net charge is 4- • Mesodesmic, polymerization • Tetrahedron can share oxygen atoms

  6. Fig. 11-1 Silica Tetrahedron

  7. Six groups of silicate minerals • Orthosilicates = Nesosilicates • Single tetrahedron • Disilicates = Sorosilicates • Two tetrahedrons share single oxygen • Ring silicates = Cyclosilicates • 4, 5, or 6 tetrahedron share two oxygen

  8. Chain silicates = Inosilicates • 2 or 3 oxygen shared, arranged in single or double chain • Sheet silicates = Phyllosilicates • 3 oxygen shared in sheets • Framework silicates = Tectosilicates • All 4 oxygen are shared

  9. Ortho- (Neso) Fig. 11-2 Chain – double and single (Ino) Di- (Soro) Ring (Cyclo) Framework (Tecto) Sheet (Phyllo)

  10. Z/O ratios • Z = Si tetrahedral sites • Can be other cations, most commonly Al • Z/O ratio depends on type of silicate • Ortho = 1/4 • Di = 2/7 • Ring = 1/3 • Chain, single = 1/3; double = 4/11 • Sheet = 2/5 • Framework = 1/2

  11. Other ions • 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

  12. Degree of polymerization depends on availability of Si • Quartz and feldspars (framework): Si-rich environments • Si/O = ½ • Olivine (orthosilicate): Si-poor environment • Si/O = ¼

  13. MaficvsFelsic • Mafic – rich in Magnesium and Iron (Ferrum), Si-poor • E.g. biotite, amphiboles, pyroxenes, and olivine • Commonly dark colored • Felsic – rich in Si and Al • E.g. Feldspars, Quartz (SiO2), muscovite, feldspathoids • Commonly light colored

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