hemimorphite, one of two minerals formerly called calamine in the U.S., a white silicate mineral that is an important zinc ore. A secondary mineral formed from the alteration of sphalerite, it is a hydrated basic zinc silicate, Zn4Si2O7(OH)2·H2O. It is associated with other zinc ores in veins and beds in limestone and occurs in many zinc mines throughout the world. Well-crystallized, sheaflike specimens have been found in Siberia; Romania; Sardinia; Belgium; and New Jersey and Montana in the United States. For detailed physical properties, see silicate mineral (table).