What is Hemimorphite?
Hemimorphite is a hydrated zinc silicate of oxidised ore zones, known for white botryoidal crusts and sky-blue radiating crystals.
Mineralogy and structure
Reference formula: Zn4Si2O7(OH)2·H2O. Hemimorphite has an orthorhombic framework and is a common secondary zinc mineral. Its botryoidal habit and association with smithsonite are useful clues, but polished blue material still needs identification. Hemimorphite belongs to the silicates and has a orthorhombic crystal system. Typical hardness is 4.5–5 on the Mohs scale and specific gravity is approximately 3.4–3.5.
Colour and appearance
Typical colours include colourless, white, blue, green. The usual tabular, botryoidal, radiating habit and vitreous, pearly lustre are useful descriptive features, but colour alone is not diagnostic.
Formation and localities
Hemimorphite forms in or is associated with oxidised zinc deposits, cavities and weathering zones above sphalerite-rich ores. Important documented localities include Mexico, China, Namibia, the United States, Slovakia and Australia.
Collecting and care
Protect botryoidal surfaces from scratches and acids; keep the specimen labelled as zinc-bearing material.
