Minerals

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Color: very variable, complex causes

Hardness: strength of atomic bonds

Density: mass and spacing of atoms

Luster: how electrons interact with light

Cleavage: weak atomic planes

Crystal Form: extremely useful but not for beginners

Other properties distinctive at times

4. Minerals can be identified by their physical properties = atomic structure

Slide 25

Color

Sometimes Distinctive

Often Unreliable

Affected By:

Chemical Impurities

Surface Coating

Grain Size

Weathering

4. Minerals can be identified by their physical properties = atomic structure

Slide 26

Hardness

Resistance to Scratching

Directly related to relative strength of atomic bonds

Scratch Test (Mohs)

Indentation Test (Knoop)

Common Errors due to:

Weathering, ‘Chalk' marks

Breaking vs. Scratching

4. Minerals can be identified by their physical properties = atomic structure

Slide 27

Mohs vs. Knoop Scales

Talc: very small

Gypsum, Fingernail: 30

Calcite, Penny: 135

Fluorite: 163

Apatite: 430

Feldspar, Glass: 560

Quartz: 820

Topaz: 1340

Corundum: 2100

Diamond: 7000

4. Minerals can be identified by their physical properties = atomic structure

Slide 28

Density

Directly related to masses of component atoms and their spacing

Usually very consistent

4. Minerals can be identified by their physical properties = atomic structure

Slide 29

Density - gm/cm3 (weight relative to water )

Air: 0.001 Wood - Balsa: 0.1, Pine: 0.5, Oak: 0.6-0.9 Gasoline: 0.7, Motor Oil: 0.9 Ice: 0.92 Water: 1.00 Sugar: 1.59 Halite: 2.18 Quartz: 2.65 Most Major Minerals: 2.6-3.0 Aluminum: 2.7

4. Minerals can be identified by their physical properties = atomic structure

Slide 30

Density

Pyrite, Hematite, Magnetite: 5.0 Galena: 7.5 Iron: 7.9 Copper: 9 Lead: 11.4 Mercury: 13.6 Uranium: 19 Gold: 19.3 Platinum: 21.4 Iridium: 22.4 (densest material on Earth)

4. Minerals can be identified by their physical properties = atomic structure

Slide 31

Luster

Metallic or Nonmetallic is the most important distinction.

Resinous, waxy, silky, etc. are self-explanatory.

Vitreous is often used for glassy luster.

4. Minerals can be identified by their physical properties = atomic structure