A mineral which has been mined from days of old from the upper parts of zinc- and lead-based ores, chiefly associated with smithsonite. It was often assumed to be the same mineral and both were classed under the same name of calamine. In the second half of the 18th century it was discovered that there were two different minerals under the heading of calamine- a zinc carbonate and a zinc silicate, which often closely resembled each other.
The silicate was the rarer of the two, and was named hemimorphite on account of the hemimorph development of its crystals. This unusual form, which is typical of only a few minerals, means that the crystals are terminated by dissimilar faces. Hemimorphite most commonly forms crystalline crusts and layers, also massive, granular, rounded and reniform aggregates, concentrically striated, or finely needle-shaped, fibrous or stalactitic, and rarely fan-shaped clusters of crystals.
Hemimorphite most frequently occurs as the product of the oxidation of the upper parts of sphalerite, accompanied by other secondary minerals which form the so-called 'iron cap' or 'gossan'. The origin is by the process of metasomatism, that is by the gradual replacement of the easily soluble limestone with less soluble matters brought by circulating waters.
The regions on the Belgian-German border are well known for their deposits of hemimorphite of metasomatic origin, especially Vieille Montagne in Belgium and Aachen in Germany. Other deposits are near Tarnovice in upper Silesia (Poland), near Phoenixville (Pennsylvania), Elkhorn (Montana), Leadville (Colorado) and Organ Mountains (New Mexico) in the USA, and in several localities in North Africa. Further hemimorphite occurences are in Nerchinsk in Siberia, Rabelj in Slovenia, Bleiberg in Carinthia (Austria), Matlock in Derbyshire (England), etc. Hemimorphite is an important ore of zinc and contains up to 54.2% of the metal