Hemimorphite

Hemimorphite, or calamine, mineral and zinc ore, of formula Zn₄Si₂O₇(OH)₂·H₂O. Hemimorphite crystallizes in the orthorhombic system (see Crystal); it has a hardness of 4.5 and a specific gravity of 3.4. Its crystals are usually white or colorless, but sometimes pale green, yellow, or blue, with a vitreous luster. It often resembles smithsonite, a zinc carbonate, with which it is frequently found in nature. British mineralogists reverse the assignment of the names hemimorphite and smithsonite. Deposits of hemimorphite occur in Mexico, the United States, and Algeria.