Mineral Information and Data:

Bassetite  
Fe2+(UO2)2(PO4)2 • 8H2O [CNMNC approved formula]

Named for the Basset mine group, Cornwall, England, from which it was first described.

IMA status : Valid species (Pre-IMA 1915) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
40.02a.16.01  
  (40) Hydrated Phosphates
  (40.02a) where A++ (B++)2 (XO4) · x(H2O), containing (UO2)++
  (40.02a.16)
  
Nickel-Strunz
(10th edition) :
08.EB.10
  (08) Phosphates, Arsenates, Vanadates
  (08.E) Uranyl Phosphates and Arsenates
  (08.EB) UO2:RO4 = 1:1
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: P21/m
Unit cell: a = 6.98Å, b = 17.07Å, c = 7.01Å; β = 90.53°
Crystal Habit: Crystals, with square or rectangular outline, to 3 mm, are thin tablets, flattened on [010], showing {111}, {101}, {110}, {001}, {010}; typically in parallel or fanlike groups.
Twinning: Two or more individuals at ~90° with [001] of one individual || [100] of the other; common.
  
Color: Olive-green, olive-brown, yellowish brown, bronzy yellow, yellow
Diaphaneity: Transparent; in transmitted light, seen as sectored due to twinning
Luster: Vitreous, bronzy on {010}
Hardness (Mohs): 2.5
Measured Density: 3.40 – 3.63 g/cm3
Cleavage: {010}, perfect; {100} and {001}, distinct
  
Geologic Setting: A rare secondary mineral in the oxidized zone of some uranium-bearing hydrothermal mineral deposits.
Mineral Association: Uranospathite, torbernite, uraninite, pyrite (Basset mines, England); meta-autunite, torbernite (Arcu su Linnarbu, Italy); saleeite, metanovacekite (Sue mine, Arizona,
USA)
  
Other Properties: Radioactive.

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