Ionic radius is related to the valence of the ion - ions that have lost electrons (cations) are smaller than their neutral state, ions that have gained electrons (anions) are larger.

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Ionic radius is related to the valence of the ion
- ions that have lost electrons (cations) are
smaller than their neutral state, ions that have
gained electrons (anions) are larger.
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If two cations are similar in ionic radius, one
may substitute for another in a mineral
structure. One of the more common substitutions
is between Fe2 (0.63 angstrom) and Mg2 (0.57)
and often a mineral contains a mixture of
bothExample is olivine - Fe2SiO4 fayalite
Mg2SiO4 forsterite olivine (Mg,Fe)2SiO4
?Ca2 and Na can also substitute for each
other in plagioclase feldspar.
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Silicates (SiO4)4- The largest mineral group due
to the fact that silicates are made up of the two
most abundant elements in the crust silicon and
oxygen. The basic building block is the silica
tetrahedra As oxygen silicon ratio decreases,
more and more silicon ions must share oxygen
atoms in order to complete their tetrahedra.
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Silicate mineralogy
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1.Isolated tetrahedra (monomer). OSi 4,
olivine is the most common example (Fe,Mg)2SiO4
no cleavage. Understand Solid solution of
Fe-Mg2.Single chain - silicate tetrahedra share
oxygens with two other tetrahedra forming a long
open ended chain. OSi 3 , pyroxenes, 2
cleavages at 90, Si2O63.Double chain two
singles chains link together so each tetrahedra
shares oxygens with three other tetrahedra. OSi
2.75, amphiboles, 2 cleavages at 60 and 120,
Si8O22
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4.Sheet silicates silica tetrahedra form large
sheets (link to three other tetrahedra) with all
of the non-shared oxygens pointing in the same
direction, Micas (biotite, muscovite)1 direction
of cleavage. O(SiAl) 2.55. Framework
silicates 3-d frameworks, all oxygens shared.
OSiAl 2. Common groups include quartz and
feldspars (potassium feldspar/orthoclase,
plagioclase). Most abundant minerals in the
earths crust. (Solid solution in
plagioclase)Can see increasing amount of SiO2
with increasing polymerization-also lower
temperature.
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• Cabonates calcite, dolomite
• Oxides magnetite, hematite
• Sulfides, sulfates, halides, native elements

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How to ID mineralsHardness Mohs
scaleSpecific gravityOther properties (fizz,
magnetic)
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Mohs scale
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Color not always!
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streak
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Crystal habit
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Cleavage-feldspars
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Cleavage
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Concoidal fracture
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Carbonates fizz