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(named after the Palygorskii section of the former Perm’ Mining District), a hydrous magnesium silicate with the approximate chemical formula Mg5[Si4O10]2(OH)2(H2O)4 · 4H2O. Part of the Mg is replaced by Al, and admixtures of Fe3+, Ca, Na, and K oxides are known to occur. According to crystal structure, palygorskite occupies an intermediate position between inosilicates and phyllosilicates. Aggregates exhibit a felted or leather-like structure and occur in the form of crusts. The monoclinic crystals, which resemble thin fibers, are white, light gray, pink, or yellow. Palygorskite has a hardness on Mohs’ scale of 2–2.5 and a density of 2,000–2,300 kg/m3. Its hardness increases substantially after roasting, and the mineral gradually loses water upon heating.
Palygorskite is mainly formed during the weathering of rocks rich in magnesium. It occurs in sedimentary rocks in the form of nests, interstratifications, and, less frequently, large individual aggregates. Palygorskite is used as heat insulation and soundproofing by the construction industry.