Minerals

Minerals: From the Inside OutMinerals are the building blocks that make up rocksThere are about 2400 known minerals.

Answer These Questions To be a mineral, all of the following questions must be

answered “yes”:

1. Is it nonliving material? A mineral is inorganic.

2. Is it formed in nature? Only naturally made crystals are classified as minerals.

3. Does it have a crystalline structure (repeating inner structure that determines shape)?

4. Is it a solid? No gases or liquids allowed.

Two Groups of MineralsMinerals are divided into two groups based on

chemical makeup:

1. Silicate minerals – contain silicon & oxygen, with additional elements; make up more than 90% of Earth’s crust.

2. Nonsilicate minerals - no silicon or oxygen but C, O, Fe, S (carbonates – calcite, halides – fluorite, oxides – corundum, sulfates - gypsum

Silicate Minerals

All silicate minerals contain the elements silicon and oxygen.

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FeldsparQuartz

Mica

Nonsilicate MineralsCA

LCIT

E

FLUO

RITE

Nonsilicate MineralsCO

RUND

UM

GYPS

UM

Identifying MineralsColor• Impurities can change color (quartz vs. amethyst)• Air and water can also change color of mineral

(pyrite is golden, but exposure turns it black)

Color

Quartz and amethyst are both silicon dioxide (SiO₂) but amethyst contains impurities which gives it

its purple color.

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Identifying Minerals (cont.)Luster• How the surface of a mineral reflects light.• Controlled by how atoms are bonded• Metallic, submetallic, nonmetallic (vitreous, silky,

resinous, waxy, pearly, earthy)

Luster

Luster

Identifying Minerals (cont.)Streak• Color of mineral in powdered form• Not always the same as color of mineral sample• More reliable than color of mineral

Hematite may vary in color but the streak will always be reddish brown.

Identifying Minerals (cont.)Cleavage and Fracture• How mineral breaks, determined by atomic

arrangementCleavage – tendency to break along flat surfaces

(mica, halite) because bonding is weakest in those directions.

Fracture – tendency to break along curved or irregular surfaces (quartz – conchoidal) when bonding is equally strong in all directions.

Identifying Minerals (cont.)Hardness• Resistance to being scratched• Mohs hardness scale:Talc, Gypsum, Calcite, Fluorite, Apatite, Orthoclase,

Quartz, Topaz, Corundum, Diamond

Scratch Test< 2.5 = Mineral marks paper2.5 = Fingernail3 = Copper Penny5 = Steel knife blade6 = Plate of glass6.5 = Steel file

Identifying Minerals (cont.)Density• How much matter there is in a given amount of

space (D = m/v) (g/ cm³)

Identifying Minerals (cont.) Special Properties

a. Fluorescence (calcite, fluorite glow under UV)b. Chemical reactions (calcite)c. Optical – calcite causes double imagesd. Taste – halitee. Magnetism – magnetic, pyrrhotite attract ironf. Radioactivity – minerals containing radium or

uranium can be detected with a Geiger counter.