Hemimorphite is a sorosilicate mineral with the formula Zn4Si2O7(OH)2-H2O It was at one time named Calamine, but confusion with another mineral led to the new name of hemimorphite, which is a reference to it's hemimorphic crystal habit. It occurs in two major forms, Clear or white thin bladed crystals, or green/blue botryoidal encrustations. This specimen is the botryoidal type, set in an iron rich matrix, and is from Santa Maria del Orto, Durango, Mexico.