Geology 284 Mineralogy Fall 2012 Dr Helen Lang West Virginia University Mineral Classification There are many possibilities biological type classification genus species Linneaus tried in 1768 but it s unsatisfactory for minerals petrologic classification o igneous minerals o sedimentary minerals o metamorphic minerals textbook organization classification by properties o This is what we use in lab by luster hardness streak etc in the Mineralogist s classification after J D Dana 1837 Minerals are grouped by their dominant anion or anionic complex Table 2 5 Perkins and handout The group to which a mineral belongs can be told directly from the chemical formula Minerals with the same anion tend to have similar properties Minerals with the same anion tend to occur together in the same geologic environment Mineral Class or Group Anion or Anionic Group Native elements no anion Ex gold Au Sulfides S Ex galena PbS Sulfosalts S As Sb Ex niccolite NiAsS bonding is mostly metallic so there is no true anion therefore no charge is given Cl F Br I Halides Ex fluorite CaF2 Ex halite NaCl O2 Oxides Ex magnetite Fe3O4 OH Hydroxides Ex brucite Mg OH 2 These have simple anions approximately spherical CO3 2 Carbonates Ex dolomite CaMg CO3 2 NO3 1 Nitrates Ex niter KNO3 BO3 2 or BO4 5 Borates Ex sinhalite MgAlBO4 These have triangular shaped complex anions SO4 2 Sulfates Ex anhydrite Ca SO4 PO4 3 Phosphates Ex apatite Silicates Ca5 PO4 3 OH SiO4 4 Ex quartz SiO2 These have tetrahedral complex anions Sketch the shape of a tetrahedron Because there are so many 800 important silicate minerals in rocks and Because silicate minerals are polymerized in many different ways The silicates are classified separately and are subdivided based on how the SiO44 tetrahedra are polymerized stuck together Silicate Mineral Subclasses See Table 2 6 Perkins and handout Isolated tetrahedral silicates nesosilicates or orthosilicates corners shared none Si O formula SiO4 4 Si O ratio 1 4 Example olivine Formula Mg2SiO4 Paired tetrahedral silicates sorosilicates corners shared 1 tetrahedron Si O formula Si2O7 6 Si O ratio 2 7 Example ackermanite Formula Ca2MgSi2O7 Ring silicates cyclosilicates corners shared 2 tetrahedron Si O formula Si6O18 12 Si O ratio 6 18 Example beryl Formula Be3Al2Si6O18 You can draw simple sketches and count Oxygens Silicons corners etc Single chain silicates inosilicates corners shared 2 tetrahedron Si O formula SiO3 2 or Si2O6 4 Si O ratio 1 3 2 6 Example diopside a pyroxene Formula CaMgSi2O6 Double chain silicates inosilicates corners shared 1 2 two 1 2 three Si O formula Si8O22 12 Si O ratio 4 11 8 22 Example tremolite an amphibole Formula Ca2Mg5Si8O22 OH 2 Hydrous contains OH Sheet silicates phyllosilicates corners shared 3 tetrahedron Si O formula Si4O10 4 Si O ratio 2 5 4 10 Example kaolinite Formula Al2Si4O10 OH 2 Hydrous contains OH Framework silicates tectosilicates corners shared 4 tetrahedron Si O formula SiO2 0 or Al Si 4O8 1 to 2 Si Al O ratio 1 2 Example quartz K feldspar Formula SiO2 KAlSi3O8