GL 107 Earth Systems Science

K. Hannula

Discussion questions for 9/3/07

1.  Define "mineral."

A mineral is a naturally-occurring, inorganic solid with an orderly internal structure and a definite chemical composition.

2.  Find three objects around your dorm room, around your house, or around town that are made of or contain a mineral (or minerals).  What minerals do they contain?

Some examples: graphite (in pencil lead), ice, halite (table salt).

3.  Find five different materials that are NOT minerals.  Why isn't each one a mineral?

Possibilities include:

Sugar - organic

Glass - no orderly internal structure

Coal - organic

Plastic - organic, man-made

Water - liquid

4.  How are minerals different from rocks?

Rocks are aggregates of minerals (or, occasionally, non-minerals such as coal or obsidian).

5.  Define each of the following properties of minerals: crystal form, luster, color, streak, hardness, cleavage, fracture, specific gravity.

Crystal form: the external shape of a crystal, controlled by its orderly internal arrangement of atoms.

Luster: The appearance of light reflected from the surface of a mineral.  Metallic and non-metallic are the two most easily-distinguished lusters.

Color: The color of transmitted or reflected light from the surface of a mineral.

Streak: The color of powdered mineral.  Can be different from color, especially for metallic minerals.

Hardness: The resistance of a mineral to scratching.  Harder minerals scratch softer minerals.

Cleavage: The tendency of some minerals to break along planar surfaces.

Fracture: The tendency of some mineral (such as quartz) to break into curved surfaces such as those in broken glass.

Specific gravity: A comparison between the weight of a mineral with the weight of an equal volume of water.

6.  Which properties of minerals are controlled mainly by their crystal structure?  Which are controlled mostly by their chemical composition?

Cleavage and crystal form are controlled mainly by crystal structure.

Specific gravity and color, although they can be controlled by structure as well, are often controlled by chemical composition.  In particular, minerals containing iron tend to be darker-colored.