<p>Classification of Minerals</p><p> Classified on the basis of anionic groups  Minerals in each group have grossly similar crystallographic properties and tend to occur in the same geological settings / environments - silicates – igneous and metamorphic rocks - carbonates – sedimentary rocks (also some igneous) - sulfides – hydrothermal systems (fluid–rock dominated) </p><p>Mineral Classes</p><p>1) Native Elements 2) Sulfides + Sulfosalts (As, Sb) S2- 3) Oxides O2- 4) Hydroxides OH- 5) Halides Cl-, F-, Br- 6) 2- Carbonates CO3 7) - Nitrates NO3 8) Borates BxOy(OH)z 9) 5- Phosphates PO4 10) 2- Sulfates SO4 11) 2- 2- Tungstates-Molybdates WO4 MoO4 12) 4- Silicates SiO4</p><p>Mineral Class  Family  Group  Species  Varieties </p><p>Silicates</p><p> 27% of all known minerals and about 40% of common rock forming minerals are silicates. Silicates make up ~ 90% of rocks in the crust of the Earth</p><p> The more important rock-forming silicate minerals include: olivine, garnet, pyroxenes, amphiboles, micas, clay minerals, feldspars and quartz (Plagioclase is the most abundant mineral in crust). Other important non-silicate rock-forming minerals include calcite and dolomite.</p><p> Important in Igneous and Metamorphic Rocks and sediments derived from them</p><p> Important elements are: Si 4+; Al3+; Fe2+; Fe3+; Mg2+; Ca2+; Na+; K+; Ti4+; Cr3+; Mn2+</p><p> Radius of Si 4+:O2-  0.26 Å  tetrahedral co-ordinated</p><p> Si-O bond is ~ 50% ionic and ~50% covalent</p><p> SiO4 has a net – 4 charge such that each oxygen has a potential to bond to another Si, thereby forming links between SiO4 tetrahedra</p><p> Silicates are classified on the basis of how the silica tetrahedral are linked</p><p> Al3+ is very important in silicates because it is the 2nd most abundant metal and the 3rd most abundant element.</p><p> Ionic Radius of Al3+ = 0.39 Å and radius ratio of Al3+:O2-  0.286 </p><p> Al3+ substitutes for Si4+ in tetrahedral sites</p><p> Because radius ratio is close to octahedral co-ordination, Al3+ can also go into the 6 co- ordinated site (octahedral)</p><p> Substitution of Al3+ into tetrahedral sites allows additional elements Mg2+; Fe2+; Fe3+; Mn2+; Cr3+; Ti4+ to be put in octahedral sites (6-fold co-ordination)</p><p> Ca2+ and Na+ go into 8-fold (cubic) sites and K+; Rb+ and Ba2+ go into 8 to 12 co-ordinated sites  General Formula for Silicate Minerals</p><p>Xm Yn (ZpOq) Wr (All formulas must be charge balanced)</p><p>8-Fold 6-Fold 4-Fold OH-, Cl-, F-</p><p>(1) -4 Nesosilicates (SiO4)</p><p>- independent tetrahedral linked by octahedral sites - O:Si = 4:1</p><p>(2) -6 Sorosilicates (Si2O7)</p><p>- two tetrahedral linked by a single oxygen atom - O:Si = 3.5:1</p><p>(3) -12 -6 Cyclosilicates (Si6O18) or (Si3O9)</p><p>- rings - O:Si = 3:1 (4) -2 Inosilicate (a) Single Chain (SiO3)</p><p>- O:Si = 3:1</p><p>-6 (b) Double Chain (Si4O11)</p><p>- O:Si = 2.75:1 (5) -2 Phyllosilicates (Si2O5) (sheet silicates)</p><p>- rings of tetrahedral linked together - O:Si = 2.5:1</p><p>(6) 0 Tectosilicates (SiO2) (3-D Framework)</p><p>- O:Si = 2:1</p>