#olmite

Olmiite

This very rare manganese silicate mineral was only recognised in 2006 by the International Mineralogical Association after beautiful mineral specimens were found, and so far it has only turned up in two mines of South Africa's Kalahari Manganese Field (Wessels and N'Chwaning ). Most new minerals only occur as tiny grains in rocks that have to be found with a microscope, but large specimens of Olmiite exist, usually forming round botyroidal aggregates of bladed wheat sheaf like crystals like this beautiful pink specimen on matrix (measuring 7.5 x 6.8 x 4 cm). A solid solution series exists with an even rarer mineral known as Poldervaarite that is the calcium end member, with our current culprit being the magnesium rich half of the duo. In reality most specimens will be somewhere along the continuum.

The crystals were born when hot and caustic hydrothermal fluids passed through a manganese deposit and metamorphosing it by adding calcium and silicon to the pre-existing elements and forming new minerals. Most specimens show a pink core (coloured by manganese) with a colourless outer rim though orange to peach and opaque to translucent white or grey aggregates are also known. It is too soft on Mohs scale for jewellery use (5.5) but specimens have been faceted for collectors. It was named after an Italian mineralogist. The (rather pricey) sample in the photo came from N'Chwaning II mine and displays 2 generations of growth.

Loz

Image credit: Rob Lavinsky/iRocks.com