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2012-2013: Physical Properties of Minerals

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J. S.

on 14 February 2013

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Transcript of 2012-2013: Physical Properties of Minerals

Physical Properties of Minerals How a mineral reflects light. Its "shine".
Vitreous (glassy)
Dull Luster 1) Cleavage – "cleave = to split".
The tendency to split along definite planes.

This relates to crystalline structure and strength of chemical bonds between atoms.

Mineral will split where bonds between atoms are weakest.

Flaky (basal) cleavage
One "plane" only. Ex. Mica and Graphite

Cleavage in two directions (2 planes)
Ex. Orthoclase feldspar

Blocky (cubic) cleavage
3 directions Exs. Galena and halite

Rhombic cleavage
3 planes not at right angles Ex. calcite

2) Fracture – Does NOT break along cleavage planes.
Can be splintery and jagged, uneven, irregular.
Or conchoidal (smooth curved surface) The Way a Mineral Splits or Breaks Easily observed, not overly useful
Example: “A red car”. Red is easy to identify, but many makes and models of cars can be red.
Many different minerals come in the same color, and many minerals come in a variety of colors.
However, some minerals do have distinctive colors, such as Malachite and Sulfur. Color Color of the powdered mineral when rubbed on an unglazed tile.
Many minerals have the same color and streak, but some are unique.
Example: Real Gold vs. Pyrite (fool’s gold)
Bite test not a good idea because
pyrite can scratch teeth!

But, pyrite’s streak is different than it’s color. Streak * The color of a mineral varies, but luster rarely does.
For example, Quartz can be purple, pink, clear, etc., but its luster is always Glassy. Resistance to scratches. NOT resistance to breakage or chipping.
Dependent on atomic arrangement and strength of bonds.
Mohs Scale of Mineral Hardness
1 is softest
10 is hardest
Samples of equal hardness can scratch each other. Hardness Mass of mineral vs.
Mass of equal volume of water Specific Gravity Mass/Volume Density ~See p. 99~ You don’t have to memorize.
Just be aware they exist.

Cubic and Hexagonal are easiest to identify
Ex: Halite Beryl

3 axes different length
intersect 90° Ex: Topaz

2 axes equal length
intersect 90° Ex: Wulfenite

3 axes different length
oblique angles Ex: Kyanite

3 axes different length
2 90°, one oblique Ex: Gypsum Crystal Forms Sulfur Malachite Pyrite Quartz (pink) Calcite Talc Hematite
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