anthophyllite, an amphibole mineral, a magnesium and iron silicate that occurs in altered rocks, such as the crystalline schists of Kongsberg, Nor., southern Greenland, and Pennsylvania. Anthophyllite is commonly produced by regional metamorphism of ultrabasic rocks. Because its fibres have a low tensile strength, anthophyllite asbestos is not as important as crocidolite or amosite and much less so than chrysotile. For chemical formula and detailed physical properties, see amphibole (table).