The International Mineralogical Association (IMA) is the generally recognized standard body for the definition and nomenclature of mineral species. Thus, for example, quartz and stishovite are two different minerals consisting of the same compound, silicon dioxide. If a chemical compound occurs naturally with different crystal structures, each structure is considered a different mineral species. Some natural solid substances without a definite crystalline structure, such as opal or obsidian, are more properly called mineraloids. A rock may consist of one type of mineral or may be an aggregate of two or more different types of minerals, spacially segregated into distinct phases. The concept of mineral is distinct from rock, which is any bulk solid geologic material that is relatively homogeneous at a large enough scale. Moreover, living organisms often synthesize inorganic minerals (such as hydroxylapatite) that also occur in rocks. However, some minerals are often biogenic (such as calcite) or organic compounds in the sense of chemistry (such as mellite). The geological definition of mineral normally excludes compounds that occur only in living organisms. In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form. For other uses, see Mineral (disambiguation).Ĭrystals of serandite, natrolite, analcime, and aegirine from Mont Saint-Hilaire, Quebec, Canada
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