Mineral IdentificationAim: How do we identify minerals?

Chapter 3: section 2

REVIEW: WHAT IS A PHYSICAL PROPERTY?

A physical property is any characteristic of a material that you can observe without changing the identity of the material.

Example: How would you distinguish pyrite (fool’s gold) from gold?

MINERAL APPEARANCE

Color Appearance

Example: Pyrite and fool’s gold are both gold in color. Gold is worth a lot of money. Pyrite has little value.

HARDNESS

Hardness is the measure of how easily a mineral can be scratched. The mineral talc is so soft you can scratch it

with your fingernail. This is the softest mineral. Diamonds are the hardest mineral.

Example: gold – hardness 2.5 - 3 pyrite – hardness 6 - 6.5

(***Do not confuse hardness with how a mineral can break***)

MOHS SCALE Friedrich Mohs

developed a list of common minerals to compare their hardnesses.

This list is called Mohs scale of hardness.

MOHS SCALE

Some minerals have a hardness range rather than a single hardness value. This is because atoms are arranged differently in different directions in their crystal structures.

LUSTER A way a mineral

reflects light is known as luster.

Luster may be metallic or nonmetallic.

Metallic – shines like a metal

Nonmetallic – glassy, dull, pearly, silky

SPECIFIC GRAVITY

Minerals can be compared by comparing the weights of equal-sized samples.

The specific gravity of a mineral is the ratio of its weight compared with the weight of an equal volume of water.

Example: Gold is 19 times heavier than water. Pyrite is 5 times heavier then water.

The tern heft describes how heavy a mineral sample feels.

STREAK When a mineral is rubbed across a piece of

unglazed porcelain tile, a streak of powdered mineral is left behind.

Streak is the color of a mineral when it is in a powdered form.

The streak test only works for minerals that are softer than the streak plate.

Example: Gold – yellow streakPyrite – greenish-black/ brownish-black streak

CLEAVAGE AND FRACTURE

Minerals that break along smooth, flat surfaces have cleavage. Cleavage like hardness is determined

partly by the arrangement of a minerals atoms.

Minerals that break with uneven, rough, or jagged surfaces have fracture.

OTHER PROPERTIES

Some minerals may have unique properties.

Magnetite – attracted to magnets