Conversations with the Earth

Tom Burbinetburbine@framingham.edu

Mineral

• A naturally occurring, homogeneous inorganic solid substance having a definite chemical composition and characteristic crystal structure

• ~4,000 known minerals– Of these, perhaps 100 can be called "common"– 50 are "occasional“– rest are "rare" to "extremely rare".

• Earth is made of minerals

• Can you name any minerals?

• Quartz – SiO2

• Diamond – C• Graphite– C• Calcite – CaCO3

• Talc - Mg3Si4O10(OH)2

Is ice a mineral?

Is ice a mineral?

• Yes, as long as it was made inorganically

Crystal Structure

• Crystalline structure - orderly three-dimensional arrangement of atoms or molecules

• Forms crystals

Color• Usually the most noticeable property• Sometimes minerals can have a wide variety of

colors

Clarity

• Transparent – clear• Translucent – foggy• Opaque – light doesn’t travel through

Crystal Form• Perfectly grown crystals can have a perfect crystal

form (e.g., cube, pyramid, prism)

Luster• How light reflects from a mineral• Metallic luster – reflects like a metal• Nonmetallic luster – doesn’t reflect like a metal

– Vitreous – like a glossy photograph– Waxy – like the luster of a candle– Satiny – like the luster of satin– Earthy – like dry soil– Greasy – like the luster of grease– Porcelaneous – like the luster of porcelain

Streak

• Color of a substance as a fine powder• A mineral is scratched on a streak plate

Hardness

• Mohs Hardness scale• 1-10 scale• Hard minerals- can scratch glass• Soft minerals –

– can’t scratch glass

Cleavage

• Cleavage – tendency of some minerals to break along flat, parallel surfaces

• Cleavage planes are parallel surfaces of weak chemical bonding

• Fracture is a break in a mineral does not occur along a cleavage plane

Tenacity

• Tenacity - resists breakage

• Brittle – shatters like glass• Malleable – like clay• Elastic – like a plastic comb• Sectile – carved with a knife

Reaction with acid

• Fizzes with cool, dilute hydrochloric acid• Carbonate minerals (minerals with CO3)• Calcite readily fizzes• Dolomite will only fizz if powdered

Striations

• Straight, hairline grooves on the cleavage surfaces• Plagioclase feldspar has striations

Magnetism

• Magnetic• Magnetite is magnetic

Specific gravity

• Density of a substance divided by the density of water

• e.g., quartz has a specific gravity of 2.65

Any Questions?