ROCK vs. MINERAL n ROCK n Mixture n Can be separated by physical means n MINERAL n Pure substance n Has specific formula n Cannot be separated by physical means

MINERAL FORMATION Geology classes

FROM A MELT n Form from lava or magma n most common method n Usually forms large crystals n example: quartz, gemstones

From a solution nEnEvaporation uHuHalite, gypsum nUnUsually soft minerals nPnPrecipitation from saturated solution uCuCalcite, barite

From Heat and Pressure nMnMainly in metamorphic rocks nCnCreates very hard minerals ugugarnet ududiamonds

From Hydrothermal n Hot watery solutions u Rain water percolates and is heated by interior of earth u Chrysocolla, azurite, gold

Classification of Minerals n Nearly 4000 minerals have been identified on Earth F Only 8 elements that make up over 98% of the Earth’s crust- THE BIG 8

ABUNDANCE OF ELEMENTS ELEMENT% BY WEIGHT OXYGEN46.6% SILICON27.7% ALUMINUM8.1% IRON5.0% CALCIUM3.6% SODIUM2.8% POTASSIUM2.6% MAGNESIUM2.1%

The silicate (SiO 4 ) -4 molecule (tetrahedron) n Wants to join with positive ions u Fe, Mg, K, Na, Al, Ca n Or joins with other tetrahedron (covalent) n Si joins tough with O = hard minerals (mostly)

Positive ions may substitute for each other n If same charge and same size u Ca and K u Fe and Mg n Use commas in formula to indicate substitution n olivine

Silicate structures- most common group of minerals Less space= harder

Olivine u Single tetrahedron u No cleavage

Pyroxene family- single chain augite2-directional clevage

AMPHIBOLE FAMILY- double chain Hornblende crystals- 2 cleavage

MICA FAMILY n Sheet silicate- one directional cleavage u MUSCOVITE u BIOTITE

Feldspar family- most common group Potassium feldspar (orthoclase)

Feldspar family Plagioclase feldspar

Quartz- Si and O only!!

Impurities n Can change color n But not chemistry!!

NON-SILICATES n Carbonates (CO 3 ) u Calcite, dolomite n Sulfates (SO 4 ) u gypsum n Halides (halogens) u fluorite n Native minerals u elements

FORMULAS n Subscripts n Parentheses n Opal n commas