Earth Minerals

Minerals

• Crystalline solid• Pure substance• Found in nature• Inorganic

Rocks

• Solid aggregate of minerals (mixtures)

Physical Properties

• Color• Luster• Cleavage• Hardness• Streak• Crystal Form• Specific Gravity• Special Properties

Color

• Most obvious characteristic of minerals

• Most unreliable characteristic for identifying minerals

• Impurities cause color variations• Example: Quartz

Luster

• Appearance or quality of light reflected from the surface of the mineral

• Descriptions:Metallic – look like metal regardless of color

Cleavage

• A minerals tendency to break along flat surfaces– Depends on the type of bond used

during the formation of mineral

• Fracture – minerals that break unevenly into curved or irregular pieces

• How to test: break the mineral

Hardness• Measure of minerals ability to resist

scratching• Does not mean resistance to cleavage or

fracture• Hardest mineral – diamond• Hardest common mineral – quartz• Softest common mineral - talc• How to test – rub mineral along a glass

slide to see if it scratches the glass or not

Streak• Color of a mineral in its powdered

form• More reliable indication of mineral

color• How to test: rub mineral against

streak plate

Crystal Form• External

expression of a mineral’s internal orderly arrangement of atoms

• How crystals will grow without interference

Specific Gravity• How dense a mineral is compared to

water• Minerals denser than water have a

density greater than 1– Quartz, feldspar, calcite, and talc – 3

specific gravity– Hematite and magnetite – 5 specific

gravity– Gold – specific gravity – 19.3 when pure

• Minerals less dense than water have a density below 1

Specific gravity…

weight of sample in air

loss of weight in waterSpecific gravity =

Special Properties

• Magnetic –– Magnetite – most common magnetic

mineral– Lodestone – type of magnetite that acts

like a magnet

• Fizzes with acid:– Calcite will fizz when hydrochloric acid is

placed on the sample– The fizz produces carbon dioxide gas

CO2

• Taste:– Mineral will have a particular taste like

salt– How do you test – lick it

• Fluorescence– Minerals absorb ultraviolet light and then

produce visible light of various colors– Calcite appears white but under UV light

appears red

• Odor – – Minerals that

smell– Sphalerite – rich

in zinc– How to test –

scratch the mineral and smell

• Double Refraction – – Light rays that bend as they pass

through the mineral– When the light bends it splits into 2 rays

and produces a double image

Mineral ID practice…What is…?1.

2.

3.

How Crystalline Minerals Form

• Evaporation of solutions– Halite and Gypsum

• Cooling of melted substances– Quartz and Olivine