Putnisite

Putnisite is a mineral composed of strontium, calcium, chromium, sulfur, carbon, oxygen and hydrogen.^[3] It was discovered on the Polar Bear Peninsula in Shire of Dundas, Western Australia in 2007 during mining activity.^[3][4] Following identification and recognition by the IMA in 2012^[4] the mineral was named after mineralogists Andrew and Christine Putnis.^[2]

Putnisite
Putnisite, from Polar Bear Peninsula, Western Australia, Australia
General
Category	Mineral
Formula (repeating unit)	SrCa4Cr83+(CO3)8(SO4)(OH)16·25 H2O
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pnma
Unit cell	a = 15.351 Å, b = 20.421 Å, c = 18.270 Å; Z = 4
Identification
Color	Purple
Crystal habit	Pseudocubic crystals
Cleavage	[100], [010] and [001] good
Fracture	Brittle - uneven
Mohs scale hardness	1.5-2
Luster	Vitreous
Streak	Pink
Diaphaneity	Translucent
Specific gravity	2.20
Optical properties	Biaxial (–)
Refractive index	nα = 1.552, nβ = 1.583 and nγ = 1.599
Pleochroism	Distinct: X pale bluish grey, Y pale purple, Z pale purple
References	[1][2][3][4]

Putnisite has unique chemical and structural properties, and does not appear to be related to any of the existing mineralogical families.^[2] Crystals are translucent purple, but show distinct pleochroism (from pale purple to pale bluish grey,^[3] depending on the angle of observation) and leave pink streaks when rubbed on a flat surface.^[3]

Putnisite occurs as small (< 0.5 mm) cube-like crystals in volcanic rock.^[2] The mineral formed during the oxidation environment within komatiite to dioritic bodies containing sulfide minerals. 

This article uses material from the Wikipedia article  Metasyntactic variable, which is released under the  Creative Commons Attribution-ShareAlike 3.0 Unported License.