Mineral Information and Data:

Aphthitalite
K3Na(SO4)2 [CNMNC approved formula]

Named from the Greek for "unalterable" and "salt" in allusion to its stability in air.

IMA status : Valid species (Pre-IMA 1813) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
28.02.02.01  
  (28) Anhydrous Acid and Sulfates
  (28.02) (A+)2 XO4
  (28.02.02)
  
Nickel-Strunz
(10th edition) :
07.AC.35
  (07) Sulfates (selenates, tellurates, chromates, molybdates, wolframates)
  (07.A) Sulfates (selenates, etc.) without Additional Anions, without H2O
  (07.AC) With medium-sized and large cations
  
Crystal system: Trigonal System
Point group (H-M): 3m (or 3 2/m) — hexagonal-scalenohedral
Unit cell: a = 5.67Å, c = 7.33Å
Crystal Habit: Crystals thin to thick tabular; pseudo-hexagonal twins resembling Aragonite; massive; crust; bladed aggregates
  
Color: Colorless(rare), white, grey, greenish, blue, or reddish due to inclusions
Diaphaneity: Transparent to opaque
Luster: Vitreous to resinous
Hardness (Mohs): 3
Measured Density: 2.66 to 2.71 g/cm3
Cleavage: 2; {1010} fair, {0001} poor
Tenacity: Brittle
Fracture: Conchoidal to uneven
Streak: White
  
Geologic Setting: An uncommon incrustation around volcanic fumaroles; a component of evaporite deposits; in guano deposits, then typically ammonian
Mineral Association: Thenardite, jarosite, sylvite, hematite (fumaroles); blodite, syngenite, mirabilite, picromerite, borax, halite (evaporites); syngenite, whitlockite, monetite, niter, gypsum (guano)
  
Other Properties: H2O Soluble. BioMineral.

 

Aphthitalite
Aphthitalite associated with halite
Origin: Kuh-E-Namak, Qom, Iran
Sample size: 7 x 5 x 3 cm
Photo: Tom Loomis

 

Aphthitalite
(zoom-in of above)

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