THE CASE OF THE SCARLETT STREAK:

MINERAL IDENTIFICATION

Virginia T. McLemore

New Mexico Bureau of Geology and Mineral Resources

New Mexico Tech

What is a mineral?

What is a mineral?• naturally occurring• inorganic• solid• homogeneous• crystalline material • with a unique chemical element or

compound with a set chemical formula• usually obtained from the ground

A crystal is composed of a structural unit that is repeated in three dimensions. This is the basic

structural unit of a crystal of sodium chloride, the mineral halite.

Why are minerals important?

Why are minerals important?

• Identification of rocks

• commodities that we use every day

• foundation of understanding geology and geologic processes that affect us everyday

• understanding geologic hazards

Minerals have distinctive physical and chemical

properties that allow for their identification.

Properties of minerals Habit (Crystal forms and

shapes) Hardness Cleavage Streak Color Luster Transparency Twinning Fracture Specific Gravity Associated Minerals

Fluorescence Magnetism Odor Feel Taste Solubility Reaction to acids Radioactive

minerals Meteoritic minerals

Hardness

Hardness• ease or difficulty with

which the mineral can be scratched

• controlled by the strength of bonds between atoms

Cleavage

Cleavage

• Way the mineral breaks or fractures

• one direction of weakness, or in other minerals, 2, 3, 4, or as many as 6 may be present

• determine the angular relation between the resulting cleavage surfaces– perpendicular– acute– obtuse

www.ironorchid.com/minerals/

From:geology.csupomona.edu/alert/mineral/minerals.htm

Streak

Streak

• color of a mineral when it is powdered

• crushing and powdering a mineral eliminates some of the effects of impurities and structural flaws

• Black - Graphite • Black - Pyrite • Black - Magnetite • Black - Chalcopyrite • Gray - Galena • Limonite - Yellow-

brown • Hematite - Red-

brown

From:geology.csupomona.edu/alert/mineral/minerals.htm

academic.brooklyn.cuny.edu/geology/leveson/core/linksa/mineral_id...

Luster

Luster• way a mineral’s

surface reflects light

• metallic• earthy• waxy• greasy• vitreous (glassy)• adamantine (or

brilliant, as in a faceted diamond)

From:geology.csupomona.edu/alert/mineral/minerals.htm

www.ironorchid.com/minerals/

Properties of minerals Habit (Crystal forms and

shapes) Hardness Cleavage Streak Color Luster Transparency Twinning Fracture Specific Gravity Associated Minerals

Fluorescence Magnetism Odor Feel Taste Solubility Reaction to acids Radioactive

minerals Meteoritic minerals

Color

From:geology.csupomona.edu/alert/mineral/minerals.htm

Habit• Crystal shape• six crystal systems• governed by the

mineral's internal structure • triclinic

• monoclinic• orthorhombic• tetragonal• hexagonal• isometric

From:geology.csupomona.edu/alert/mineral/minerals.htm

Specific Gravity

• specific gravity

– ratio of mineral density to the density of water

• similar to weight

• density – ratio of the mass of a mineral to its volume

academic.brooklyn.cuny.edu/geology/leveson/core/linksa/mineral_id...

academic.brooklyn.cuny.edu/geology/leveson/core/linksa/mineral_id...