Silicates SiOn silicon oxide

1/3 of all minerals are silicates

about 95% of the Earth’s crust is composed of silicates

Earth’s Crust Chemical CompositionELEMENT WEIGHT%

O (oxygen) 47Si (silicon) 28Aluminum 8Fe (iron) 5Ca (calcium) 4Na (sodium) 3K (potassium) 3Mg (magnesium) 2

Total 98.5%

Average Mineral Crustal Composition Mineral Weight%

feldspar * 66 *quartz * 10 *magnetite/hematite 6

Ferromagnesium minerals *

(olivine, pyroxene, amphibole, biotite) 15 *

Total 97

*silicate

Other important minerals

muscovite (mica) gypsumclays halitecalcite dolomite

MINERAL IDENTIFICATION

Primarily based on physical properties.

The properties of each mineral are determined by:

chemical elements present

arrangement of elements in the mineral structure

Streak (scratchability)Color of powdered mineral

Specific gravity Au gold PbS galena

Density - mass/volume

Specific gravity - mass of sample / mass of equal volume of water

Cleavage

planar surfaces caused by breaks along planes of weakness in atomic structure.

Number of directions and angle important.

Cleavage

cleavage

Cleavage

FractureIrregular surfaces caused by breaks

Crystal formExternal morphology due to atomic

structure. Quartz and corundum

have 6 crystal faces.

Luster

The way in which light is reflected, e.g., metallic, glassy

Color

Poor except for metallics and silicate varieties

Hardness Mohs Hardness Scale

1. Talc2. Gypsum

2.5 finger nail 3.5 penny

3. Calcite4. Fluorite5. Apatite

5.0 nail 5.0-6.0 glass and knife blade

6. Orthoclase (feldspar) 7. Quartz 8. Topaz 9. Corundun10. Diamond

Striations Striations odormagneticDouble Refraction

Mineral Resources

Ore -- mineral that can be mined for a profit

Gangue --worthless minerals in

an ore body

examples of oresAg silverAu goldCopper sulfides (covellite)Fe oxides (hematite)PbS lead sulfide (galena)

The U.S.A imports about 80% of the most used 16 metals!