Mineral Information and Data:

Anhydrite
CaSO4 [CNMNC approved formula]

Named from the Greek for without water.

IMA status : Valid species (Pre-IMA 1795) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
28.03.02.01  
  (28) Anhydrous Acid and Sulfates
  (28.03) (A++) XO4
  (28.03.02)
  
Nickel-Strunz
(10th edition) :
07.AD.30
  (07) Sulfates (selenates, tellurates, chromates, molybdates, wolframates)
  (07.A) Sulfates (selenates, etc.) without Additional Anions, without H2O
  (07.AD) With only large cations
  
Crystal system: Orthorhombic System
Point group (H-M): mmm (or 2/m 2/m 2/m) — dipyramidal
Unit cell: a = 6.238 Å, b = 6.991 Å, c = 6.996 Å
Crystal Habit: Crystals equant, thick tabular or prismatic, rare; usually massive, granular
Twinning: On {011}; rare on {120}
  
Color: Colorless, white, gray, bluish, violet, pink, red, brown
Diaphaneity: Transparent to translucent
Luster: Vitreous to greasy to pearly
Hardness (Mohs): 3.5
Measured Density: 2.98 g/cm3
Cleavage: 3; {010} perfect, {100} nearly perfect, {001} good to imperfect
Tenacity: Brittle
Fracture: Uneven to splintery
Streak: White or grayish white
  
Geologic Setting: A major component in sedimentary evaporite deposits and in the cap rocks above salt domes, commonly formed by dehydration of gypsum; in igneous rocks, fumarolic deposits, and in seafloor hydrothermal chimneys, also an alteration product in hydrothermal mineral deposits.
Mineral Association: Gypsum, halite, sylvite, polyhalite, dolomite, calcite, magnesite, celestine, sulfur
  
Synonyms/varieties: Anhydrous Gypsum, Anhydrous Sulfate of Lime, Karstenite, Karstenite
Other Properties: Gemstone Extremely Rare.

 

Anhydrite
Anydrite with some calcite on the back
Origin: Naica, Chihuahua, Mexico
Sample size: 3.5 x 1.5 x 5.5 cm
Photo: Dan Weinrich

 

Anhydrite
Anhydrite crystals with fluorite
Origin: Campiano Mine, Tuscany, Italy
Sample size: 6.7 x 3.5 x 2.1 cm
Photo: Dan Weinrich

 

Anhydrite
(zoom-in of above)

 

Anhydrite
Origin: Bad Ischl, Salzkammergut, Austria
Sample size: 10 x 9 x 5 cm
Photo: Rob Lavinsky

 

Anhydrite
(zoom-in of above)

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