ROCK vs. MINERAL

ROCK Mixture Can be

separated by physical means

MINERAL Pure

substance Has specific

formula Cannot be

separated by physical means

MINERAL FORMATION

Geology classes

FROM A MELT

Form from lava or magma

most common method

Usually forms large crystals

example: quartz, gemstones

From a solution

Evaporation Halite, gypsum

Usually soft minerals

Precipitation from saturated solution Calcite, barite

From Heat and Pressure

Mainly in metamorphic rocks

Creates very hard minerals

garnet diamonds

From Hydrothermal

Hot watery solutions Rain water

percolates and is heated by interior of earth

Chrysocolla, azurite, gold

Classification of Minerals

Nearly 4000 minerals have been identified on Earth

Only 8 elements that make up over 98% of the Earth’s crust- THE BIG 8

ABUNDANCE OF ELEMENTS

ELEMENT % BY WEIGHT

OXYGEN 46.6%

SILICON 27.7%

ALUMINUM 8.1%

IRON 5.0%

CALCIUM 3.6%

SODIUM 2.8%

POTASSIUM 2.6%

MAGNESIUM 2.1%

The silicate (SiO4)-4 molecule (tetrahedron)

Wants to join with positive ions Fe, Mg, K, Na, Al, Ca

Or joins with other tetrahedron (covalent) Si joins tough with O = hard minerals (mostly)

Positive ions may substitute for each other If same charge and same size

Ca and K Fe and Mg

Use commas in formula to indicate substitution

olivine

Silicate structures- most common group of minerals

Less space= harder

Olivine Single tetrahedron No cleavage

Pyroxene family- single chain

augite 2-directional clevage

AMPHIBOLE FAMILY- double chain Hornblende crystals- 2 cleavage

MICA FAMILY Sheet silicate-

one directional cleavage MUSCOVITE BIOTITE

Feldspar family- most common group Potassium feldspar (orthoclase)

Feldspar family Plagioclase feldspar

Quartz- Si and O only!!

Impurities

Can change color

But not chemistry!!

NON-SILICATES

Carbonates (CO3) Calcite, dolomite

Sulfates (SO4) gypsum

Halides (halogens) fluorite

Native minerals elements

FORMULAS

Subscripts Parentheses Opal commas