What is Cahnite?
Cahnite is a rare calcium boro-arsenate with tetragonal symmetry, known for colourless to white pseudo-tetrahedral crystals and cruciform twins.
Mineralogy and structure
The reference formula is Ca2B(AsO4)(OH)4. Cahnite belongs to the borates and crystallises in the tetragonal system. Cahnite is almost universally twinned on {110}; interpenetrating twins can produce a characteristic cross-like outline. Because it contains arsenate, specimens should be handled as display minerals only.
Colour and appearance
Typical colours include colourless, white and golden brown. For small or complex mineral species, crystal size, transparency, lustre and matrix association are often more diagnostic than colour alone.
Formation and localities
Cahnite forms in or is associated with manganese-rich metamorphic ore bodies, skarns and borate-arsenate cavities. Important documented localities include Franklin in New Jersey, the type locality, Norway, Namibia and Turkey. A precise mine or geological setting is preferable to a broad country label when it is known.
Collecting and care
Cahnite is best treated as a labelled reference or collector specimen. Protect fragile crystals from impact and humidity changes. Arsenic-, cadmium-, lead-, thorium- and selenium-bearing minerals should not be cut, ground or used in jewellery; wash hands after handling and keep them away from food and children.
