IDENTIFYING MINERALS

Mineral Identification

Geologist test physical and chemical properties to identify minerals Color Luster Texture Streak Hardness Cleavage and Fracture Density and Specific Gravity Special Properties

Color

A mineral’s color is a result of chemical composition and presence of trace elements

Many minerals can be found in more than one color or shade

Example – Quartz can be found in several different forms

Jasper

Has traces of iron oxides giving it a red tinge

Amethyst

Contains ferric iron making it purple

Citrine

Contains iron hydrates making them orange

Rose Quartz

Contains manganese or titanium

Color is the most obvious characteristic of a mineral but it is also the least reliable.

Luster

How the surface of a mineral reflects light

Two main categories Metallic – mineral shines like chrome Nonmetallic – minerals do not shine

More specific type of nonmetallic Dull Pearly Waxy Silky

Texture

How a mineral feels to the touch Smooth Rough Ragged Greasy Soapy Glassy Texture test is perhaps the most subjective

Streak

The color of the mineral in powder form Tested by rubbing the mineral across an

unglazed Streak color is not always the same as

the mineral color in rock form Example – pyrite is gold in rock form but

has a greenish-black streak

Streak cont.

Different variations of a mineral have the same streak Example – Flourite can be purple, yellow,

green, or blue but the streak is always white

When can this test not be used? When the minerals are harder than a

porcelain plate

Hardness

A measure of how easily a mineral can be scratched.

Measured on the Moh’s Hardness Scale One of the best identification tests 1-10 scale: Talc is the softest, diamond is

the hardest Common objects can be used to measure

hardness

Mineral Moh’s Scale Hardness

Hardness of Common Object

Talc 1 (softest)

Gypsum 2 Fingernail (2.5)

Calcite 3 Piece of copper (3.5)

Flourite 4 Iron nail (4.5)

Apatite 5 Glass (5.5)

Feldspar 6 Steel file (6.5)

Quartz 7 Streak plate (7)

Topaz 8 Scratches quartz

Corundum 9 Scratches topaz

Diamond 10 (Hardest) Scratches all common materials

Cleavage and Fracture

Both describe how a mineral breaks Cleavage – splits easily and evenly along

flat planes Mica

Fracture – breaks with rough, jagged edges Quartz

Density and Specific Gravity

Density Very good identification tool Mass divided by volume Density is different than weight

Consider two different amounts of the same mineral

Their weights would be different Their densities would be equal

Specific Gravity Ratio of the weight of a substance to the

weight of an equal volume of water at 4° C

Special Properties

Some minerals have unique physical and chemical properties Double Refraction – light bends in two directions

when it passes through the mineral Magnetism – mineral is naturally magnetic

magnetite Odor – sulfide produces a rotten-egg smell when

rubbed on streak plate Fizzes – chemical reaction to acid or other

solutions Calcite and hydrochloric acid

Taste

ORES AND GEMS

Ores

A useful mineral can be mined for a profit

Examples Hematite – source of iron Bauxite – source of aluminum Rutile – source of titanium

Gems

Are nothing more than minerals that are valuable simply because they are prized for their rarity and beauty Examples – Diamonds, Rubies, Amethyst