Minerals may be identified by their color (though this often varies because of impurities), hardness (measured on Moh's scale), luster, specific gravity, crystal forms and cleavage; or by chemical analysis and X-ray diffraction. Minerals are generally classified by their anions (negative ions) – in order of increasing complexity: elements, sulfides, oxides, halides, carbonates, nitrates, sulfates, phosphates, and silicates. Others are classed with those which they resemble chemically and structurally, e.g., arsenates with phosphates. A newer system classifies minerals by their topological structure.
Minerals sometimes occur in veins. Rocks, such as granite or sandstone, are mixtures of minerals. Their compositions can vary widely and cannot be approximated by a mineral formula.
Related category GEOLOGY AND PLANETARY SCIENCE
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