Putnisite Explained

Putnisite
Formula:SrCa4Cr83+(CO3)8(SO4)(OH)16·25 H2O
Imasymbol:Pni[1]
Class:Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Symmetry:Pnma
Unit Cell:a = 15.351 Å,
b = 20.421 Å,
c = 18.270 Å; Z = 4
Color:Purple
Habit:Pseudocubic crystals
Cleavage:[100], [010] and [001] good
Fracture:Brittle – uneven
Mohs:1.5–2
Luster:Vitreous
Refractive:nα = 1.552, nβ = 1.583 and nγ = 1.599
Opticalprop:Biaxial (−)
Pleochroism:Distinct: X pale bluish grey, Y pale purple, Z pale purple
Streak:Pink
Gravity:2.20
Diaphaneity:Translucent
References:[2] [3] [4] [5]

Putnisite is a mineral composed of strontium, calcium, chromium, sulfur, carbon, oxygen and hydrogen.[4] It was discovered on the Polar Bear Peninsula in Shire of Dundas, Western Australia in 2007 during mining activity.[4] [5] Following identification and recognition by the IMA in 2012[5] the mineral was named after mineralogists Andrew and Christine Putnis.[3]

Putnisite has unique chemical and structural properties, and does not appear to be related to any of the existing mineralogical families.[3] Crystals are translucent purple, but show distinct pleochroism (from pale purple to pale bluish grey,[4] depending on the angle of observation) and leave pink streaks when rubbed on a flat surface.[4]

Putnisite occurs as small (< 0.5 mm) cube-like crystals in volcanic rock.[3] The mineral formed during the oxidation environment within komatiite to dioritic bodies containing sulfide minerals.[4]

Notes and References

  1. Warr. L.N.. 2021. IMA–CNMNC approved mineral symbols. Mineralogical Magazine. 85. 3 . 291–320. 10.1180/mgm.2021.43 . 2021MinM...85..291W . 235729616 . free.
  2. https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Putnisite Mineralienatlas
  3. Web site: New Mineral Shows Nature's Infinite Variability . University of Adelaide. 26 April 2014.
  4. Putnisite . Mineralogical Magazine . February 2014 . 78 . 1 . 131–144 . 10.1180/minmag.2014.078.1.10 . 26 April 2014 . Elliott . P. . 102242056 . subscription .
  5. Web site: Putnisite: Putnisite mineral information and data . Mindat.org . 2014-04-07 . 2014-04-29.