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Mineral Encyclopedia – illite

Illite is a layered clay mineral similar to mica, also known as hydromuscovite. The flaky or strip-like crystals of illite are very small, and they generally appear to us as earthy. Because of impurities, illite is generally yellow, brown, green and other colors, but if the purity is high, it should be white. Much illite is formed by weathering of muscovite or potassium feldspar, and illite can be transformed into other clay minerals. The crystals are mainly monoclinic hydrous layered silicate minerals. In the formula, R2+ represents divalent metal cations, mainly Mg2+﹑Fe2+ and so on. The crystal structure is basically the same as that of muscovite, and it also belongs to the 2-octahedral type of the 2:1 structural unit layer. Crystals have polymorphic variants such as 1M, 2M, 1Md and 3T. Unlike muscovite, the amount of K+ in the interlayer is less than that of muscovite, and there are water molecules. Therefore illite is also called water muscovite. Others use…