Mineral Information and Data:

Bassanite
CaSO4 • 0.5H2O [CNMNC approved formula]

Named for Francesco Basani (185301916). Italian paleontologist, University of Naples, Italy.

IMA status : Valid species (Pre-IMA 1910) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
29.06.01.01  
  (29) Hydrated Acid and Sulfates
  (29.06) where A XO4 · x(H2O)
  (29.06.01)
  
Nickel-Strunz
(10th edition) :
07.CD.45
  (07) Sulfates (selenates, tellurates, chromates, molybdates, wolframates)
  (07.C) Sulfates (selenates, etc.) without Additional Anions, with H2O
  (07.CD) With only large cations
  
Crystal system: Monoclinic System
Point group (H-M): 2 — sphenoidal
Space group: I2
Unit cell: a = 12.0317(4) Å, b = 6.9269(2) Å, c = 12.6712(3) Å; b = 90.27(1)° Z = 12
Crystal Habit: As needle-like crystals, to 0.1 mm, typically in parallel aggregates.
Twinning: About [010], twin plane {101}, may be sectored (synthetic)
  
Color: White
Diaphaneity: Semi-transparent
Luster: Dull
Measured Density: 2.69 - 2.76 g/cm3
  
Geologic Setting: Altered from gypsum in leucite tephrite blocks; fumarolic (Vesuvius, Italy); in dry or perennially dry lake beds (California USA; Australia); in caves, interlayered with gypsum
Mineral Association: Gypsum, anhydrite, celestine, calcite, gibbsite
  

 

Bassanite
Bassanite after gypsum
Origin: Taft, Kern Co., California, U.S.A.
Sample size: Microscopic image
Photo and Owner: Lou Perloff

 

Bassanite
White bassanite pseudomorphous after gypsum
Origin: Tolbachik volcano, Kamchatka Oblast', Far-Eastern Region, Russia
Picture size: 4 mm
Photo and owner: Thomas Witzke

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