What is Cairncrossite?
Cairncrossite is a hydrated calcium strontium sodium phyllosilicate from the Wessels manganese mine in South Africa.
Mineralogy and structure
The reference formula is Sr2Ca7-xNa2x(Si4O10)4(OH)2·(H2O)15-x. Cairncrossite belongs to the silicates and crystallises in the triclinic system. Its triclinic structure combines silicate sheets with calcium octahedral layers and intercalated strontium-sodium polyhedra. The variable x in the formula reflects natural chemical substitution and hydration.
Colour and appearance
Typical colours include colourless to white. For small or complex mineral species, crystal size, transparency, lustre and matrix association are often more diagnostic than colour alone.
Formation and localities
Cairncrossite forms in or is associated with manganese-rich metamorphic ore and complex hydrothermal alteration zones. Important documented localities include Wessels Mine in the Kalahari Manganese Field, South Africa. A precise mine or geological setting is preferable to a broad country label when it is known.
Collecting and care
Cairncrossite 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.
