SMITHSONITE and HEMIMORPHITE (thumbnail)

Smithsonite, or zinc spar, is the mineral variant of zinc carbonate (ZnCO3). Initially, it was confused with hemimorphite until it was established that they are distinct minerals. Their similar appearances led to the use of the term calamine for both, causing some misunderstanding. The name smithsonite was given in 1832 by François Sulpice Beudant to honor the English scientist James Smithson, who first described the mineral in 1802.

This trigonal mineral exhibits a range of colors and is rarely found in well-formed crystals, typically appearing as earthy botryoidal masses. It has a Mohs hardness of 4.5 and a specific gravity ranging from 4.4 to 4.5.

Hemimorphite is a chemical compound represented by the formula Zn4(Si2O7)(OH)2·H2O and is a constituent of the mineral calamine. This silicate mineral, along with smithsonite (ZnCO3), has been historically extracted from the upper regions of zinc and lead ores. Initially, both minerals were thought to be identical and categorized under the name calamine. However, in the latter part of the 18th century, it was determined that these distinct compounds coexisted within calamine, despite their close resemblance.