Putnisite

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 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 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.[3]

References

  1. ↑ Mineralienatlas
  2. 1 2 3 4 "New Mineral Shows Nature's Infinite Variability". University of Adelaide. Retrieved 26 April 2014.
  3. 1 2 3 4 5 6 "Putnisite". Mineralogical Magazine. Retrieved 26 April 2014.
  4. 1 2 3 "Putnisite: Putnisite mineral information and data". Mindat.org. 2014-04-07. Retrieved 2014-04-29.


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