Download Classification of Minerals

Classification of Minerals
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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)
Mineral Classes
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
Native Elements
Sulfides + Sulfosalts (As, Sb)
Oxides
Hydroxides
Halides
Carbonates
Nitrates
Borates
Phosphates
Sulfates
Tungstates-Molybdates
Silicates
S2O2OHCl-, F-, BrCO32NO3BxOy(OH)z
PO45SO42WO42- MoO42SiO44-
Mineral Class  Family  Group  Species  Varieties
Silicates
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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
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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.
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Important in Igneous and Metamorphic Rocks and sediments derived from them
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Important elements are: Si 4+; Al3+; Fe2+; Fe3+; Mg2+; Ca2+; Na+; K+; Ti4+; Cr3+; Mn2+
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Radius of Si 4+:O2-  0.26 Å
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Si-O bond is ~ 50% ionic and ~50% covalent
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SiO4 has a net – 4 charge such that each oxygen has a potential to bond to another Si,
thereby forming links between SiO4 tetrahedra
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Silicates are classified on the basis of how the silica tetrahedral are linked
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Al3+ is very important in silicates because it is the 2nd most abundant metal and the 3rd
most abundant element.
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Ionic Radius of Al3+ = 0.39 Å and radius ratio of Al3+:O2-  0.286
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Al3+ substitutes for Si4+ in tetrahedral sites
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Because radius ratio is close to octahedral co-ordination, Al3+ can also go into the 6 coordinated site (octahedral)
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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)
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Ca2+ and Na+ go into 8-fold (cubic) sites and K+; Rb+ and Ba2+ go into 8 to 12 coordinated sites
 tetrahedral co-ordinated
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General Formula for Silicate Minerals
Xm Yn (ZpOq) Wr
8-Fold 6-Fold
4-Fold
(All formulas must be charge balanced)
OH-, Cl-, F-
(1) Nesosilicates (SiO4)-4
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independent tetrahedral linked by octahedral sites
O:Si = 4:1
(2) Sorosilicates (Si2O7)-6
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two tetrahedral linked by a single oxygen atom
O:Si = 3.5:1
(3) Cyclosilicates (Si6O18)-12 or (Si3O9)-6
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rings
O:Si = 3:1
(4) Inosilicate (a) Single Chain (SiO3)-2
- O:Si = 3:1
(b) Double Chain (Si4O11)-6
- O:Si = 2.75:1
(5) Phyllosilicates (Si2O5)-2 (sheet silicates)
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rings of tetrahedral linked together
O:Si = 2.5:1
(6) Tectosilicates (SiO2)0 (3-D Framework)
- O:Si = 2:1