2.3 Properties of Minerals

Textbook pp 50-55

Properties of Minerals

• The differences among minerals is what we use to identify them.

Color • While color is unique to some minerals, this

property is often not useful in identifying many minerals. Small amounts of different elements can give the same mineral different colors.

Sapphire

Streak • Streak is the color of a mineral in its

powdered form. Streak is obtained by rubbing a mineral across a streak plate, a piece of unglazed porcelain.

• While the color of a mineral may vary from sample to sample, the streak usually doesn’t. Therefore, a streak can be a good indicator.

Luster

• Luster is used to describe how light is reflected from the surface of a mineral.

Minerals that have the appearance of metals, regardless of their color, are said to have a metallic luster.

Pyrite

• Minerals with a nonmetallic luster are described by many adjectives.

Vitreous/ Glassy

Earthy

Pearly

Crystal Form

• Crystal form is the visible expression of a mineral’s internal arrangement of atoms. Every mineral has a distinct crystal form.

• What shape might you call the crystal blocks of this pyrite?

Hardness • One of the most useful properties used to

identify a mineral is hardness.

• Hardness is a measure of the resistance of a mineral to being scratched.

• You can find this property by rubbing the mineral against another mineral of known hardness.

Cleavage • Cleavage is the

tendency of a mineral to cleave, or break down, along flat, even surfaces.

• This break tends to be along the weakest part of a mineral’s structure.

Fracture

• Minerals that do not show cleavage when

broken are said to fracture. Fracture is the uneven breakage of a mineral.

• Do you think this calcite would have a cleavage or a fracture when broken?

Density

• Density is a property of all matter that is the ratio of an object’s mass to its volume.

• The density of a pure mineral is a constant value, so it can be used to determine the purity or identity of some materials.

Some minerals have very distinctive properties. Calcite has what is called double refraction, which means that although it is transparent, it doubles the image of whatever is behind it.

• Sulfur smells like rotten eggs, so streaks of a mineral that contains sulfur will smell like rotten eggs as well.

• Magnetite and hematite are magnetic, and will attract paper clips and small nails.

A mineral’s properties depend upon:

-the elements that compose the mineral (its composition)

-its structure (how its minerals are arranged.

• What are some of the properties we can use to identify this mineral specimen?