What is Nantokite?
Nantokite is a soft cubic cuprous chloride from reducing parts of copper deposits, famous for its instability in moist air.
Mineralogy and crystal structure
Reference formula: CuCl. Nantokite has a cubic cuprous-halide structure but rapidly alters in oxygen and moisture to green copper chlorides and other products. Fresh colourless material is therefore difficult to preserve. Nantokite is classified with halides and has a cubic crystal system. Typical hardness is 2.5–3 on the Mohs scale and specific gravity is approximately 4.1–4.2.
Colour, lustre and habit
Typical colours include colourless, white, grey, green. The usual cubic, granular, crusty habit and vitreous, resinous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Nantokite forms in or is associated with reducing zones of copper sulfide deposits, mine workings and chloride-rich hydrothermal environments. Important documented localities include Chile, Germany, Cornwall, Australia, Mexico and the United States.
A fleeting colourless copper chloride
Nantokite is a mineral preservation challenge: its simple cubic structure is stable only in the right chemical environment, and humidity can transform a fresh crystal into a green alteration crust.
Collecting and care
Keep sealed, cool and dry; avoid water, air exposure and all abrasive handling.
