Crystals of putnisite (purple) . Image credit: P. Elliott et al.
The new mineral is named putnisite after Drs Christine and Andrew Putnis from the University of Münster, Germany, for their outstanding contributions to mineralogy.
Putnisite occurs as isolated pseudocubic crystals, up to 0.5 mm in diameter, and is associated with quartz and a near amorphous Cr silicate.
It is translucent, with a pink streak and vitreous lustre. It is brittle and shows one excellent and two good cleavages parallel to {100}, {010} and {001}.
“What defines a mineral is its chemistry and crystallography. By x-raying a single crystal of mineral you are able to determine its crystal structure and this, in conjunction with chemical analysis, tells you everything you need to know about the mineral,” explained Dr Elliott, who, along with colleagues, described putnisite in the Mineralogical Magazine.
“Most minerals belong to a family or small group of related minerals, or if they aren’t related to other minerals they often are to a synthetic compound – but putnisite is completely unique and unrelated to anything.”
Putnisite combines the elements strontium, calcium, chromium, sulfur, carbon, oxygen and hydrogen:
The mineral has a Mohs hardness of 1.5–2, a measured density of 2.20 g/cm3 and a calculated density of 2.23 g/cm3. It was discovered during prospecting by a mining company in Western Australia.
“Nature seems to be far cleverer at dreaming up new chemicals than any researcher in a laboratory,” Dr Elliott concluded.
P. Elliott et al. 2014. Putnisite, SrCa4Cr83+(CO3)8SO4(OH)16•25H2O, a new mineral from Western Australia: description and crystal structure.Mineralogical Magazine, vol. 78, no. 1, pp. 131-144; doi: 10.1180/minmag.2014.078.1.10

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