Anhydrite occurrence, Huancarqui District, Castilla Province, Arequipa, Peru
Anhydrite forms irregular concretions with a thin milky white crust, commonly up to about 15 cm in diameter. It comes from sedimentary rocks at Huanquarque, near Aplao, 65 km NNE of Camana, in Arequipa department. Anhydrite colour is blue-gray, density 2.96, hardness 3.5, refr. index 1.55.Ref: J. Hyrsl, Gemstones of Peru, 2012, p. 35