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30 Oct 2010
Jan 30th 2009
Minerals vs. rocks
- A rock is a naturally formed, consolidated material composed of grains of one or more minerals
- A mineral is a naturally occurring, inorganic, crustalline solid that has a definite chemical
- These are the building blocks of rocks
o To identify minerals in a rock, a thin section is often needed
o E.g. a rock can consist of clear Quartz, pink Feldspar, and black Biotite
- The most important group are the silicate minerals containing silicon and oxygen and accounts
for 90% of all minerals
- A few dominated minerals include:
o Quartz (silica = SiO2 = silicon + oxygen
o Olivine (Mg, Fe SiO4)
o Feldspars
o Pyroxenes (e.g. augite)
o Mica
o Clay minerals (e.g. kaolinite, montmorillonite)
Silicon-oxygen tetrahedron: SiO4 -4
- 4 oxygen around a silicon molecule
o Source of cooling magma
- This is the building block for 90% of minerals on earth
- As magma cools, its chemistry changes
o Chemistry of a rock shows how much time it has taken to cool
o E.g. igneous rocks are instantly cooled in MORs
o XPXoµ}vWuPuZ}o]](]Á]Z}µZ]vPZZ[µ(~o}vP]u}
cool deep in the earth)
Tetrahedrons clump together
o Changes behaviour of magma
E.g. viscosity
More tetrahedrons causes high viscosity
x Forms strato volcanoes that are dangerous
How do we identify different minerals?
- Colour
o Most noticeable, least accurate!
- Streak
o Colour when mineral ground to a fine powder on a rough ceramic plate
E.g. hematite t red/brown
o Silicate minerals do not streak
Hardness (scratchability)
- D}Z[Zvo-10)
o Talc (very soft) = 1
o Gypsum = 2
o fingernail
o Calcite = 3
o Copper coin
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