Transcript What is a mineral? "A mineral is a naturally occurring, homogeneous

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.
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 both
Example is olivine - Fe2SiO4 = fayalite;
Mg2SiO4 = forsterite; olivine = (Mg,Fe)2SiO4
Ca2+ and Na+ can also substitute for each
other in plagioclase feldspar.
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.
Silicate mineralogy
1.Isolated tetrahedra (monomer). O:Si = 4, olivine
is the most common example (Fe,Mg)2SiO4 no
cleavage. Understand Solid solution of Fe-Mg
2.Single chain - silicate tetrahedra share oxygens
with two other tetrahedra forming a long open
ended chain. O:Si = 3 , pyroxenes, 2 cleavages at
~90, Si2O6
3.Double chain: two singles chains link together so
each tetrahedra shares oxygens with three other
tetrahedra. O:Si = 2.75, amphiboles, 2 cleavages
at 60 and 120, Si8O22
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:(Si+Al) = 2.5
5. Framework silicates: 3-d frameworks, all
oxygens shared. O:Si+Al = 2. Common groups
include quartz and feldspars (potassium
feldspar/orthoclase, plagioclase). Most abundant
minerals in the earth’s crust. (Solid solution in
plagioclase)
Can see increasing amount of SiO2 with
increasing polymerization-also lower temperature.
• Cabonates: calcite, dolomite
• Oxides: magnetite, hematite
• Sulfides, sulfates, halides, native elements
How to ID minerals:
Hardness: Moh’s scale
Specific gravity
Other properties (fizz, magnetic)
Moh’s scale
Color not always!
streak
Crystal habit
Cleavage-feldspars
Cleavage
Concoidal fracture
Carbonates fizz