COLOR

• Color is not usually a definitive property of a mineral. Color will only be definitive is it is a major constituent in the mineral.– A good example of this is malachite which is green from the Cu.

• However most minerals have a variety of colors.

Some Colors of Quartz

STREAK

• For opaque minerals, if you rub the sample across a streak plate, it will leave a colored powder. This streak is distinctive for minerals and is used to identify minerals.

Varieties of Hematite

• For example, plagioclase, variety labradorite– Interference of light either at the surface or in

the interior of a mineral--series of color--much the same as oil on water. Opal is another example.

Play of Colors: Iridescence

Plagioclase-variety Labradorite

LUSTER

• Metallic or non-metallic

• Non-metallic: vitreous or glassy; silky; resinous; pearly; greasy; waxy, dull; earthy

Examples of metallic luster

Example of non-metallic luster

• Vitreous--quartz

Example of non-metallic luster

• Silky--example satinspar

Example of non-metallic luster

• Resinous--sphalerite

Example of non-metallic luster

• Pearly--Talc

Example of non-metallic luster

• Dull--Kaolinite

Example of non-metallic luster

• Earthy--Goethite (limonite)

Example of non-metallic luster

• Waxy--serpentine

LUMINESCENCE

• The emission of light not due to incandescence. For example, fluorescent minerals colors under ultraviolet light. Minerals include varieties of calcite, fluorite and scheelite.

The fluorite on your left is fluorescingThe fluorite on your right is the correct color

Hardness• The resistance

a mineral has to being scratched. It is measured on a qualitative scale called the Mohs’ Hardness scale.

Cleavage• The Tendency

of a mineral to split along planes parallel to the crystal faces, leaving smooth flat surfaces in one or more directions

Fracture• If a mineral

doesn’t have cleavage it will have fracture. That is it will not break with flat even surfaces. There are many types of fracture.

Fracture continued

• Some adjectives used to describe fracture are: hackly = very jagged

• even = smooth but not flat

• uneven = rough & irregular but

• not sharp or jagged

• conchoidal = broken glass look

Acid Test

• A weak solution of HCl is placed on a mineral to see if it reacts. The reaction is would be a fizzing or bubbling on the surface of the mineral. That means the mineral is a carbonate, likely a limestone or calcite

Other Properties

• Some other mineral properties:

• Taste

• Specific gravity

• Smell

• flexibility

Identification

• No one mineral property by itself can be trusted to identify the mineral. It is the combination of mineral properties that are used for identification.