Mineral definition and classification

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To be classified as a "true" mineral, a substance must be a solid and have a crystal structure. It must also be an inorganic, naturally-occurring, homogeneous substance with a defined chemical composition. The chemical composition may vary between end members of a mineral system. For example the plagioclase feldspars comprise a continuous series from sodium-rich albite (NaAlSi₃O₈) to calcium-rich anorthite (CaAl₂Si₂O₈) with four recognized intermediate compositions between. Mineral-like substances that don't strictly meet the definition are sometimes classified as mineraloids. Other natural-occurring substances are Nonminerals. Industrial minerals is a market term and refers to commercially valuable mined materials (see also Minerals and Rocks section below).

A crystal structure is the orderly geometric spatial arrangement of atoms in the internal structure of a mineral. There are 14 basic crystal lattice arrangements of atoms in three dimensions, and these are referred to as the 14 "Bravais lattices". Each of these lattices can be classified into one of the six crystal systems, and all crystal structures currently recognized fit in one Bravais lattice and one crystal system. This crystal structure is based on regular internal atomic or ionic arrangement that is often expressed in the geometric form that the crystal takes. Even when the mineral grains are too small to see or are irregularly shaped, the underlying crystal structure is always periodic, and can be determined by X-ray diffraction.

Chemistry and crystal structure together define a mineral. In fact, two or more minerals may have the same chemical composition, but differ in crystal structure (these are known as polymorphs). For example, pyrite and marcasite are both iron sulfide, but their arrangement of atoms differs. Similarly, some minerals have different chemical compositions, but the same crystal structure: for example, halite (made from sodium and chlorine), galena (made from lead and sulfur) and periclase (made from magnesium and oxygen) all share the same cubic crystal structure.

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RT @acarvin: About 2/3rds of the additives are vitamins and minerals; the remaining additives are there to counteract against any flavors they'd add.
purplesofa (Leslie Grable) Tue, 31 Jan 2012 20:04:30 -0000
RT @acarvin: About 2/3rds of the additives are vitamins and minerals; the remaining additives are there to counteract against any flavors they'd add.
About 2/3rds of the additives are vitamins and minerals; the remaining additives are there to counteract against any flavors they'd add.
acarvin (Andy Carvin) Tue, 31 Jan 2012 20:04:09 -0000
About 2/3rds of the additives are vitamins and minerals; the remaining additives are there to counteract against any flavors they'd add.
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