Lecture Twenty - Rocks and minerals in geochemical reactions

Question 1

Define a rock and a mineral.

Answer 1

A rock is a solid, naturally occurring aggregate of minerals.
A coherent, naturally occurring solid consisting of an aggregate of minerals or, less commonly, a mass of glass.

A mineral is a naturally occurring crystalline solid with a definite, but not necessarily fixed, chemical composition.
It may be produced by biological or biologically - mediated chemical reactions but is typically inorganic in composition (no C-C bonds).

Question 2

What are the major mineral groups?

Answer 2

Define on a chemical bases (mainly).
Typically named for anions (negatively charged part of the minerals structure).
Na7ve elements Oxides Sulphides Sulphates Carbonates Halides Phosphates Silicates

Native elements - Cu, Au, Ag 
Oxides - Magnetite, Fe3O4 
Sulphides - Pyrite, FeS2 
Sulphates - Gypsum, CaSO4.2H2O
Carbonates - Calcite, CaCO3
Halides - Halite, NaCl; Fluorite, CaF2 
Phosphates - Fluorapatite, Ca5(PO4)3F
Silicates  - Quartz, SiO2

Question 3

What is the difference between minerals and chemicals?

Answer 3

Minerals are chemical compounds.
Minerals are a naturally occurring, inorganic subset.
Therefore, minerals can participate in geochemical reactions.
They may be reagents and products of geochemical reactions.

Question 4

When do geochemical reactions occur?

Answer 4

Minerals or the fluids from which minerals may form are subjected to changes in T, P and/or composition of fluid (hydrothermal, magma, water, air, supercritical gasses).

A mineral out of equilibrium with T, P and/or composition of its environment will reaction.