Properties of Minerals

What is a mineral?• A naturally occurring, inorganic solid that

has a crystal structure and a definite chemical composition.

• More than 3,000 identified minerals.• About 20 minerals make up most of the

Earth’s crust.

Characteristics of a mineral

1. Naturally occurring

2. Inorganic

3. Solid

4. Crystal structure

5. Definite Chemical composition.

Naturally Occurring

• Mineral must occur naturally on Earth– Gold, copper, silver, graphite

Inorganic• The mineral cannot arise from materials

that were once part of a living thing

• Coal occurs naturally in the Earth’s crust, but it comes from the remains of plants and animals that lived millions of years ago.

Solid• A mineral is always solid, with a definite

volume and shape.

Crystal Structure

• The particles of a mineral line up in a pattern that repeats over and over again.

• A crystal has flat sides, called faces, that meet at sharp edges.

Definite Chemical Composition• A mineral always contains certain

elements in definite proportions– For example, the mineral of quartz has one

atom of silicon for every two atoms of oxygen.

How do we identify a mineral?

• Each mineral has its own specific properties that can be used to identify it.

1. Hardness

2. Color

3. Streak

4. Luster

5. Density

6. Breaking

Hardness• In 1812, Friedrich Mohs, a mineral expert,

invented a test to describe and compare the hardness of minerals.

• The scale ranks ten minerals from softest to hardest.

• A mineral can scratch any mineral softer than itself.

Mohs Hardness Scale

Color• Color can be used to identify only those few

minerals that always have their own characteristic color.– Malachite is always green– Azurite is always blue

• Many minerals, however, like quartz, can occur in a variety of colors.

Streak• A streak test can provide a clue to a

minerals identity.• The streak of a mineral is the color of its

powder.• You can observe a streak by rubbing a

mineral against a streak plate.

Luster• Luster is the way a mineral reflects light

from its surface.

• Minerals containing metals are often shiny.

• Other minerals, such as quartz, have a glassy luster.

Density• No matter what the size of a mineral, the

density of that mineral always remains the same.

• You must determine the mass of the mineral (on a balance)

• You then place the mineral in water, to see how much it displaces.

• The volume of the displaced water, equals the volume of the mineral.

Testing Density

Rocks mass = 300 ounces

Displaces water by 100 cm3

So volume of rock must be 100 cm3

D = MU 300 V 100

D = 100 g/cm3

Breaking Properties

Cleavage

• Mineral breaks along a flat surface or into sheets

Fracture

• When a mineral breaks with lots of jagged edges

Special Properties that work….Sometimes…

1. Fluorescence– Fluorescent color under ultraviolet (UV) light

2. Magnetic– Attract magnets

3. Acid reaction– Carbon dioxide gas bubbles off when you

drop acid on them– Carbonates!

Fluorescence

Magnetic

Carbonate Acid Reaction