Chapter 3

Minerals and Rocks

Earth Materials

Minerals• A mineral is a naturally occurring,

homogeneous solid of definite chemical composition and ordered atomic arrangement that is usually formed by inorganic processes.

• A Natural Crystalline Phase

Minerals• A mineral must occur naturally.• It must be chemically homogeneous

down to the atomic level• It must have a chemical formula (eg

SiO2, FeS2)

• It must have a defined crystal structure.• It must be inorganic (not the result of

biological processes alone).

Some Familiar Minerals

• Quartz (SiO2)• Pyrite (FeS2)• Calcite (CaCO3)• Gold (Au)• Silver (Ag)• Copper (Cu)• Diamond (C)• Graphite (C)

• K-feldspar (KAlSi3O8)• Na-feldspar (NaAlSi3O8)• Olivine (Mg2SiO4)

• Garnet (Mg3Al2Si3O12)

• Gypsum (CaSO4 2H2O)• Apatite (Ca5 (PO4)3OH)

• Ice (H2O)• Halite (NaCl) (Salt)

Hydrothermal Gold

Occurrence: Evaporites, Salt Domes

Uses: Table salt, De-icing, Nuclear waste host rock?

Halite NaCl (Salt)

Calcite CaCO3

Ice H2O

Quartz SiO2

Quartz SiO2

Mineral Properties

• Hardness (Mohs Scale)• Luster• Color• Shape• Density

Some Non-Mineral Solids

• Obsidian (Glass)• Opal (Amorphous)• Coal (Amorphous)• Wood (Organic)• Amber (Organic)

Polymorphs

• Same composition - different structure– Graphite - Diamond (C)– Quartz - Tridymite - Cristobalite - Coesite– Calcite - Aragonite (CaCO3)

– Pyrite - Marcasite (FeS2)

Isomorphs

• Same Structure - Different Composition– Olivine (Mg2SiO4) (Fe2SiO4)

– Calcite - Rhodochrosite (CaCO3) (MnCO3)

– Apatite (Ca5(PO4)3OH) - (Ca5(PO4)3F)

Rocks are Composed of Minerals

A Rock is an Aggregate of Minerals

• Igneous - – Crystallized from melts– Surface - Volcanic; Subsurface -

Intrusive

• Sedimentary - – Deposited from air and water on the

surface

• Metamorphic– Recrystallized from pre-existing

igneous or sedimentary rocks.