A new mineral, Putnisite, was discovered in 2007 on the Polar Bear Peninsula in Western Australia. This purple-pink mineral is unique in its mineral structure, and unlike any of the ~4,000 known minerals.
Putnisite – SrCa4Cr83+ (CO3)8SO4(OH)16·23H2O – is comprised of strontium, calcium, chromium, sulphur, carbon, oxygen and hydrogen. While it was discovered in 2007, it wasn’t finally classified until 2012, and named after Australian mineralogists Andrew and Christine Putnis.
This unusual mineral is unique in both chemical composition and crystal formation. The cube-like crystals have several hues of translucent purple and also exhibit distinct pleochroism. Pleochroism is an optical phenomenon in which the mineral appears to be different colours when observed at different angles, especially with polarized light. Putnisite varies from a pale purple to a pale bluish grey. The mineral has been reported to leave a trail of bright pink streaks when abrasion occurs.
While prospecting for nickel and gold was underway, explorers noticed the striking pink grains. Samples were sent to the Commonwealth Scientific and Industrial Research Organization (CSIRO), and later sent to Peter Elliot at the South Australian Museum for examination and description.
“Putnisite, a strontium calcium chromium sulphate carbonate, has both a unique chemical composition and a unique crystal structure,” Mr Elliot said. Found on volcanic rock, Putnisite occurs as tiny crystals of just 0.5mm in diameter.
A detailed description of the mineral can be found at Mineralogical Magazine.