Composition of the Earth        

The Earth is made up of all the elements listed in the periodic table. The main rock forming elements are:

O      (47%) Mg     (2%)
Si      (28%) Ca      (3.5%)
Al     (8%) Na      (3%)
Fe    (5%) K         (2.5%)
Other elements (84)    (1%)

Combinations of these elements form minerals, which in turn, when combined, form rocks. Rocks are identified by the minerals they contain.

Common minerals and their formula:

Quartz SiO2
Pyrite FeS2
Plagioclase Feldspar Na/Ca Alumino-Silicate
Calcite   CaCO3
Muscovite Mica Pottasium Alumino-Silicate
Augite Ca/Mg/Fe rich Alumino-Silicate
Horneblende Ca/Mg/Fe rich Alumino Silicate
Biotite Mica Fe/Mg rich Alumino-Silicate
Olivine  Fe Mg Silicate
Orthoclase Feldspar  Pottasium Alumino-Silicate
Garnet Fe rich Alumino-Silicate

image of Earth taken from