Minerals of Earth’s CrustChapter 5

What is a mineral? A natural, usually inorganic solid that has a

characteristic chemical composition, an orderly internal structure, and a characteristic set of properties

Halite

Characteristics of Minerals1. Inorganic

2. Forms and exists in nature

3. Crystalline solid (atoms are arranged in a regular pattern)

4. Consistent chemical composition

Gypsum

Fluorite

Mineral or Nonmineral?

Mineral or Nonmineral?

Salt?Sugar?

Ice?

Charcoal? Rock?

Kinds of Minerals• Scientists have identified 3,000 minerals• Of those minerals, there are 20 common rock-

forming minerals• All minerals are divided into 2 main groups:

Silicate and Nonsilicate Minerals

SilicatesNonsilicates

Silicate Minerals• Minerals that contain a combination of silicon and oxygen

atoms

• Silicate minerals other than quartz have one or more additional elements such as Ca, Na, K, Fe, or Mg

• Silicate minerals make up 96% of Earth’s crust

• Quartz and feldspar make up more than 50% of the crust

Nonsilicate Minerals• Minerals that do not contain a combination of

silicon and oxygen atoms• Nonsilicate minerals make up 4% of Earth’s crust• There are 6 major classes of nonsilicate minerals

Classification of Nonsilicate Minerals

How to Identify Minerals

Mineralogists identify minerals based on a number of specific physical properties:ColorStreakLusterCleavage and FractureHardnessCrystal ShapeDensity

Color• Easy to observe• Unreliable on its own• Trace amounts of

certain elements can greatly effect color of some minerals (ex: sapphires and rubies)

• Weathering can also cause changes in color

Rubies are cut from corundum with traces of Chromium (Cr)

Sapphires are cut from corundum with traces of Cobalt (Co)

Streak• Color of the mineral

in the powder form• More reliable than

color• Use a streak plate:

unglazed tile• Minerals that are

harder than the streak plate will leave no streak

Luster• Light reflected from the mineral’s surface• Metallic luster reflect light like polished metals• All other minerals have nonmetallic luster:

waxy, pearly, glassy, dull/earthy, or virtuous/brilliant

Cleavage and Fracture• Cleavage is the

tendency of a mineral to split along specific planes of weakness to form smooth, flat surfaces

• Cleavage occurs in one, two, or three directions

Cleavage in three directions. Example: CALCITE

Cleavage and Fracture

• Fracture is when the mineral does not split along cleavage planes

• Fracture can be irregular, fibrous, or conchoidal

Hardness• A measure of the ability

of a mineral to resist scratching

• Hardness does NOT mean resistance to cleavage planes!!

• Hardness relates to the strength of bonds between the minerals atoms (Ex: Diamond vs. Graphite)

Moh’s Hardness Scale

• To determine an unknown mineral’s hardness, you need to scratch it against a mineral of known hardness

Crystal Shape• A mineral always has the same basic crystal shape

because the atoms that make up the mineral always combine in the same geometric pattern

• There are 6 basic crystal systems that can become more complex due to conditions during formation

Density• Ratio of mass to volume

of a substance

Density = mass/volume

• Helps identify heavier minerals more readily than it helps identify lighter ones

• Most minerals have a density between 2 and 3 g/cc Galena

Density = 7.6 g/cc

Lead

Density = 11.35 g/cc

Special Properties of MineralsSome minerals

exhibit special properties that can also be used for identification such as:

FluorescencePhosphorescenceDouble RefractionMagnetismRadioactivity