Geol 101 - Mineral Identification

What is a mineral?

What is a mineral?

a naturally occurring inorganic substance that is solid at room temperature and has a distinct chemical composition + well-defined crystalline structure.

How many common rock-forming minerals are there?

Less than 30. (95% of Earth’s Crust)

Crystalline Structure

Arrangement of atoms that is repeated to form a mineral grain.

Crystal Habit

Crystals that grow slowly in open space to develop a characteristic form.

How many mineral groups are there?

8

How are the mineral groups sorted by?

Chemical Composition

Ferromagnesian Silicates

Iron/Magnesium that is dark colored; dense.

Non-ferromagnesian Silicates

Calcium/Aluminum/Potassium that is light colored; light weight

What are diagnostic physical properties?

Hardness, luster, streak, specific gravity, cleavage/fracture, tenacity and special properties.

Hardness

ability of a solid substance to resist permanent deformation when subjected to a compressive force.

Diaphaneity

Passage of light through a mineral.

1. Transparent

2. Translucent

3. Opaque

Color

Useful when looking at distinctive coloration that can be used for identification.

Streak

a small sample is dragged across a sample of an unglazed ceramic plate, leaving a streak of powdered material. The streak reveals the actual color of a mineral.

Tenacity

Toughness; how the mineral behaves in response to bending.

Cleavage

How a mineral breaks along one or more weak planes within the crystalline structure.

Fracture

Minerals breaking roughly; no flat surfaces.

Crystal Shape/Habit

geometric form that displays how a crystal grew under unobstructed conditions.

Luster

the way that light reflects, or doesn’t, from the surface of a material.

How to identify an unknown mineral sample?

1. Look at the mineral ID chart for luster

2. Examine fractures/cleavage

3. Estimate hardness

How many cleavages does this mineral have?

One; Samples are split into thin sheets along that one plane.

How many cleavages does this mineral have?

Two; Samples are split into thin sheets along two planes.

How many cleavages does this mineral have?

Three; Right angles right to each other, breaks into cubes.

How many cleavages does this mineral have?

Three; Not right angles, breaks into rhombohedrons.