MINERALS

What is a mineral?

ORDERED ATOMIC STRUCTURE

Emerald (beryl)

DISORDERED ATOMIC STRUCTURE

Beer bottles, windows (glass)

Ions are bonded together to form minerals

Halite (NaCl)

Physical Properties of Minerals

- depends on chemical composition and crystal composition • Luster

• Hardness

•Form/Habit

• Density

• Cleavage/Fracture

• Streak

Diamond (C) Graphite (C)

Metallic Luster

Galena

Pyrite

(= like metal)

Non-Metallic Luster (Vitreous = like glass)

Halite Quartz

Streak (color of mineral in powdered form)

only useful for metallic minerals

hematite

Cleavage

Fracture (uneven broken surface = like plate glass)

Examples: Obsidian; quartz

External Crystal Forms

Reaction w/ dilute HCl (or vinegar)

Calcite (CaCO3) = vigorous reaction on all surfaces

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

Density and Specific Gravity

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

• Specific Gravity (G) = mass of mineral ÷ mass of equivalent volume of H2O at 1 atm and 4ºC.

= ρmineral / ρwater; ρwater = 1; and thus G ≈ ρmineral

Other Properties

1. magnetism (only for magnetite)

2. color (helpful, but not diagnostic)