Description
The mineral hemimorphite (also called calamine) is a hydrated zinc silicate with the chemical formula Zn4Si2O7(OH)2·H2O. It belongs to the sorosilicates. The mineral occurs primarily as an oxidation product in the upper layers of zinc blende deposits. Well-known deposits include the Belgian-German border, Silesia in Poland, and the states of Pennsylvania and Missouri in the United States. Hemimorphite is one of the most common sorosilicates. Its most notable characteristic is its polar or hemimorphic crystals, from which it gets its name. The crystal structure has a different termination at each end of the crystal. One termination, the "bottom," is rather blunt and dominated by a pedion face, while the other end, the "top," is terminated by the point of a pyramid. The crystal structure contains tetrahedrons of ZnO3OH, interlocked with Si2O7 groups and water molecules. The zinc is at the center of the tetrahedron, while the three oxygen atoms, along with an OH group, are at the four points of the tetrahedron. The tetrahedra are all aligned in the same direction, with a plane parallel to the pedion termination and the "apex" of the tetrahedra pointing toward the pyramidal termination.
