Minerals

What is a mineral?

• Inorganic – not alive• Solid – not liquid, or gas• Naturally occurring

– not formed by man, but nature

• Definite chemical composition– Elements always the same, with known

arrangement

• Definite crystal shape – Repeating pattern of atoms in 3D

Formation of Minerals

• Magma cooling– Slow cooling – large crystals– Fast cooling – small crystals– Very fast cooling - no crystals

• Solution evaporation– Salts and geodes

• Common elements– Si, Al,Ca, K, O2, Fe, Na, Mg

Minerals Everyday

• Mineralogists – study minerals

• Rocks are combinations of minerals

• Ores- rocks from which valuable minerals are removed (usually metals)

• Gems – rare, “pretty,” not soft– Diamonds, rubies, emeralds

Luster

• Way the surface reflects light • General: Metallic and Non-metallic• More specific:

– Vitreous (glassy) -- example: quartz, tourmaline – Adamantine (brilliant) -- example: diamond – Resinous (like resin or sap from a tree) -- example:

sphalerite – Greasy or waxy -- example: turquoise – Pearly -- example: talc – Silky -- example: asbestos – Dull or earthy -- example: bauxite

Crystal Shape

• Arrangement of atoms form crystal structure

• Types-– Cubic– Orthorhombic– Tetragonal– Hexagonal– Triclinic– Monoclinic

Color

• Easily identifiable trait – but,not reliable

• Color can change– Impurties - Yellow diamonds– Oxidation – rusting, tarnish– Weathering

Streak

• mineral is rubbed firmly across a white tile– it leaves a line of powder.

• color of the streak is always the same

• Example:– quartz leaves a white streak, whether it's

violet (amethyst), pink (rose quartz), or brown (smoky quartz).

Transparency

• how well light passes through a mineral

• Three degrees of transparency:– Transparent – you can see through– Translucent – see light , but not objects– Opaque - can't see anything

Hardness

• Mohs Hardness Scale - 1812

• Scale used to tell how hard (10) or soft (1) a mineral is

• Commonly used substitutes:– Fingernail – 2.5– Penny – 3.5– Glass – 5.5

Hardness Mineral

1 Talc (Mg3Si4O10(OH)2)

2 Gypsum (CaSO4·2H2O)

3 Calcite (CaCO3)

4 Fluorite (CaF2)

5 Apatite (Ca5(PO4)3(OH-,Cl-,F-))

6 Orthoclase Feldspar (KAlSi3O8)

7 Quartz (SiO2)

8 Topaz (Al2SiO4(OH-,F-)2)

9 Corundum (Al2O3)

10 Diamond(C)

Hardness Mineral Associations and Uses

1 Talc Talcum powder.

2 Gypsum Plaster of paris. Gypsum is formed when seawater evaporates from the Earth’s surface.

3 Calcite Limestone and most shells contain calcite.

4 Fluorite Fluorine in fluorite prevents tooth decay.

5 Apatite When you are hungry you have a big "appetite".

6 Orthoclase Orthoclase is a feldspar, and in German, "feld" means "field".

7 Quartz  

8 Topaz The November birthstone. Emerald and aquamarine are varieties of beryl with a hardness of 8.

9 Corundum Sapphire and ruby are varieties of corundum. Twice as hard as topaz.

10 Diamond Used in jewelry and cutting tools. Four times as hard as corundum.

2.5Fingernail

2.5–3 Gold, Silver

3 Copper penny

4-4.5 Platinum

4-5 Iron

5.5 Knife blade

6-7 Glass

6.5 Iron pyrite

7+ Hardened steel file

Hardness of some other items:

Cleavage

• When broken minerals break along planes of weakness– Related to crystalline structure– Some break along 1 plane, others 2 planes

Fracture

• The way a mineral without cleavage breaks

• Not all minerals cleave easily

• Some fracture– can be smoothly curved, irregular, jagged or

splintery.

Specific Gravity is the ratio of the density of a material compared to the density of water 1g/ml. Materials greater

than 1 will sink. Materials less will float.

• Density of the mineral

Mineral Density Specific Gravity

Graphite Light 1-2

Quartz Medium 2-3

Fluorite, beryl Medium Heavy

3-4

Cordrundum, most metals

Heavy 4-6

Gold, platinum Heaviest 19

Special Properties to ID minerals

• Taste – salt, NaCl

• Smell – sulfur, S

• Magnetic – magnetite

• Fluorescent – glow in the dark (UV)

• Optical double vision - calcite