Achávalite
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Achávalite is a selenide mineral that is a member of the nickeline group. It has only been found in a single Argentinian mine system, being first discovered in 1939 in a selenide deposit. The type loc
Black metallic crystals of achávalite from Cacheuta Mine, Mendoza, Argentina
Mineral
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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 i
Crystals of serandite, natrolite, analcime, and aegirine from Mont Saint-Hilaire, Quebec, Canada
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).
Hübnerite, the manganese-rich end-member of the wolframite series, with minor quartz in the background
When minerals react, the products will sometimes assume the shape of the reagent; the product mineral is termed 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.