MINERALS

What is a mineral?

Naturally occurring, inorganic solid with an orderly crystalline structure and chemical composition

1. Naturally occurring = by natural geologic processes (ex: cooling of feldspars in magma) not man made; cubic zirconium)

2. Solid

3. Orderly, repetitive structure (in terms of arrangement of atoms; Opal or glass are not minerals for this reason).

4. Definite chemical composition (represented by chemical formulas like SiO2 )

5. Generally inorganic (not produced from living things; CaCO3 = calcium carbonate or Calcite is an exception; makes up shells of marine animals).

Mineral Formation

1. Crystallization from magma - Iron, magnesium, and calcium minerals 1st; then sodium, potassium, quartz minerals

2. Precipitation of solid mineral when water evaporates out.

3. Pressure and temperature - cause metamorphism = changes in pressure and temperature that allow minerals to migrate and react with each other in new ways --> form new minerals.

4. Hydrothermal Solutions - Hot mixture of dissolved substances

Physical Properties of Minerals

- depends on chemical composition and crystal composition • Color

• Streak

• Luster

• Density

•Hardness

• Crystal Form

• Cleavage/Fracture

Color: Helpful, but not nec. diagnostic; some minerals have a colored varieties

Corundum’s structure is the same. Trace amounts of different element produce a variety of colors. Red = Ruby; Blue = Sapphire

http://socrates.berkeley.edu/~eps2/wisc/jpeg/l8sj49.jpeg

Streak: color of mineral in powdered form

only useful for metallic minerals

hematite

Tested by…

Streak plate – rub mineral across white tile.

Streak not nec. Same as color.

Metallic Luster Galena Pyrite

(= like metal)

Non-Metallic Luster: (Vitreous = like glass)

Halite & Quartz

Luster = How mineral’s surface reflects light

Diamond (C)

Graphite (C)

Crystal Form: How atoms are arranged internally

Platy minerals = flat like sheets (ex. Muscovite)

Hexagonal = quartz

Calcite = rhomboid

Galina = cubes

Hardness: Resistance to being scratched

Can be scratched by glass, but not penny = Moh’s hardness of 4-6

Cleavage & Fracture: tendency of a mineral to break along flat, even surfaces

Cleavage: Minerals break along the planes of their weak bonds.

Perfect Cleavage = Micas (muscovite & biotite) = cleave along 1 plane. Results = sheets

Halite = 2 cleavage planes

Fracture: uneven breaking of mineral surface; conchoidal- no cleavage pattern

Cleavage

Reaction w/ acid

- will fizz in calcium minerals.

Calcite (CaCO3) = vigorous reaction on all surfaces

Dolomite (Ca,Mg)CO3= mild reaction on powder; scratch then add acid

Density = mass/volume (gm/cm3; typical range 2 to 8 gm/cm3)

Magnetism (magnetite) – Contains iron

Flourescence = Minerals give off wavelengths in U.V.