Putnisite, a new mineral

Geologists in Australia have discovered a new mineral, putnisite (photo above by P. Elliott, G. Giester, R. Rowe, and A. Pring).

Putnisite has the chemical formula SrCa4Cr8(CO3)8SO4(OH)16·25H2O. The chromium in the mineral is trivalent, so that’s 2 + 2×4 + 3×8 = 34 for cations and 2×8 + 2 + 16 = 34 for anions. See here for the crystal structure. Putnisite is quite soft, with a hardness of 1½–2 on the Mohs scale.

Related minerals include strontianite: SrCO3, celestine: SrSO4, and the purple stichtite: Mg6Cr2CO3(OH)16·4H2O, which was also discovered in Australia (photo below by Didier Descouens).

Putnisite was found at Lake Cowan, near Norseman, Western Australia, and was named after Münster-based mineralogists Andrew and Christine Putnis. The discovery was published earlier this year. Peter Elliott, the lead author of the paper, is a visiting research fellow in the School of Earth and Environmental Sciences at the University of Adelaide, as well as a research associate with the South Australian Museum.

I’m sure that the Museum would love a specimen for their collection (photo below), although the crystals of putnisite found so far are in fact almost microscopically small.

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  1. Pingback: 2014 in review | Scientific Gems

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