Minerals

5.2 Composition and Structure of Minerals

What is a mineral?

• A mineral has the following characteristics:– It occurs naturally.– It is a solid.– It has a definite chemical composition.– Its atoms are arranged in an orderly pattern.– It is inorganic (never alive or produced by

something that was alive.)

Minerals

• There are about 4000 known minerals– Examples) gold,

quartz, halite (salt), diamond

• 8 elements make up 98.5% of the crust’s total mass.

• Most minerals are compounds.

Name Symbol %Oxygen O 46.6

Silicon Si 27.7Aluminum Al 8.1

Iron Fe 5.0Calcium Ca 3.6Sodium Na 2.8Potassium K 2.6Magnesium Mg 2.1

Other - 1.5

Minerals Through the Magma Process

• Many minerals form out of molten rock.• In magma, atoms or ions can move freely.• As magma cools the atoms, molecules and ions

move closer together and form chemical bonds that create compounds.

• Many different minerals can form from the same magma mass.

• The types of minerals that form depend on:– The types of elements present in the magma– The rate at which the magma cools determines the

crystal size.

Minerals Through the Pressure Process

• When a rock is subjected to high temperature and pressure, the minerals begin to break down chemically.

• The temperature and pressure becomes great enough to change the mineral in a solid state.

• The free atoms, ions, and molecules recombine forming new minerals.

Structure of Minerals

• Minerals form crystals.– A regular geometric solid with smooth

surfaces called crystal faces.– Contain a regularly, orderly arrangement of

atoms.

• Although there are thousands of different minerals, there are only 6 basic different shapes of crystals.

Six Crystal Systems

Silicates

• Silicon and oxygen are the two most abundant elements in the Earth’s crust.

• Most minerals (90%) contain these two elements and are called silicates.

• A silicate may contain one or more metallic elements.

• The basic building block of a silicate is the silicate tetrahedron.– Consists of 4 oxygen atoms around a silica atom.– Named for its shape.

Silica Tetrahedron