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What The Earth Is Made Of - Minerals and Rocks


For more information, follow the link "To Rocks" below.

The eight most common elements in the earth are (by weight):

Oxygen (46%)
Silica (27.7%)
Aluminum (8.1%)
Iron (5%)
Calcium (3.6%)
Sodium (2.8%)
Potassium (2.6%)
Magnesiun (2%)

Minerals are comprised of various elements, but some single elements are also minerals. The definition of a mineral is:

A mineral is a naturally occuring, homogeneous, solid with a crystalline atomic structure. Crystallinity implies that a mineral has a definite and limited range of composition, and that the composition is expressible as a chemical formula. Some definitions of minerals give them as inorganic materials, however both diamonds and graphite are considered minerals, and both are primarily comprised of carbon, which would make them organic. So this leads me, as an engineer, to believe that mineralogists do not have a good, precise definition of a mineral, but rather a loose definition. The definition above, is the most inclusive and would include all substances currently described as minerals. The key items that make something a mineral are occurring naturally, and the definite crystal structure, that is expressible as a chemical formula. Rocks that do not meet this criteria are referred to as amorphis - not having a definite structure or expressible as a chemical formula. Some elements that occur naturally and are minerals are arsenic, bismuth, platinum, gold, silver, copper, and sulphur.

Minerals are formed as both simple compounds and complex compounds. A simple compound has a balance of electron charge, there is no net charge on the mineral, each (-) electron is balanced with a positive charged cation (+). Complex minerals have a imbalanced net charge of either (-) negative or (+) positive.

Minerals are further broken down into categories such as:

Oxides - which are positive charged cations paired with oxygen, such as Hematite (Fe2O3) and quarts (SiO2)

Sulfides - which are positive charged cations paired with sulfur, such as Galena (PbS), and Pyrite (FeS)

Halides- which are defined as a salt of any halogen acid, such as halite (NaCl).
Halogens are (F2, Cl2, Br2, and I2).
Carbonates - which is defined as a cation paired with a carbonate (CO3), such as Calcite (CaCO3) and Siderite (FeCO3)

Sulfates - which are defined as a cation paired with a sulfate (SO4), such as Barite (BaSO4) and Gypsum (CaSO4).

Silicates - which are defined as a cation paired with a silicate (SiO4), such as Albite (NaAlSiO4) and Orthite (CaAlSiO4)

Mafic Minerals - which are defined as iron and magnesium (FeMg), such as Olivine ((FeMg)3(AlSi2) and Biotite K(MgFe)2 (AlSi3)O10

Clay Minerals - which are defined as weathered silicates


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