Guiné-Bissau Minerals and Volcano Souvenir Sheet of 5 Stamps MNH
A mineral is a naturally occurring chemical compound, usually of crystalline form and not produced by life processes. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids. The study of minerals is called mineralogy.
As of March 2018, there are more than 5,500 known mineral species; 5,312 of these have been approved by the International Mineralogical Association (IMA).
Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, which were determined by the mineral's geological environment when formed. Changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals. Within a mineral species there may be variation in physical properties or minor amounts of impurities that are recognized by mineralogists or wider society as a mineral variety, for example amethyst, a purple variety of the mineral species quartz.
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