Mineral
![Amethyst, a variety of quartz](/Images/godic/202412/19/Améthystre_sceptre24208.jpg")
![Schist is a metamorphic rock characterized by an abundance of platy minerals. In this example, the rock has prominent sillimanite porphyroblasts as large as 3 cm (1.2 in).](/Images/godic/202412/19/Sillimanite-1996714208.jpg")
![Hübnerite, the manganese-rich end-member of the wolframite series, with minor quartz in the background](/Images/godic/202412/19/Hubnerite-Quartz-2164554208.jpg")
![When minerals react, the products will sometimes assume the shape of the reagent; the product mineral is termed to be a pseudomorph of (or after) the reagent. Illustrated here is a pseudomorph of kaolinite after orthoclase. Here, the pseudomorph preserved the Carlsbad twinning common in orthoclase.](/Images/godic/202412/19/Kaolinite-Orthoclase-lw18c4208.jpg")
A mineral is a naturally occurring substance, representable by a chemical formula, that is usually solid and inorganic, and has a crystal structure. It is different from a rock, which can be an aggregate of minerals or non-minerals and does not have a specific chemical composition. The exact definition of a mineral is under debate, especially with respect to the requirement a valid species be abiogenic, and to a lesser extent with regard to it having an ordered atomic structure. The study of minerals is called mineralogy.