Mineral Information and Data:

Colemanite
CaB3O4(OH)3 • H2O [CNMNC approved formula]

Named after William Tell Coleman (1824–1893), pioneer developer of the borax industry in California, USA.

IMA status : Valid species (Pre-IMA 1883) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
26.03.05.01  
  (26) Hydrated Borates Containing Hydroxyl or Halogen
  (26.03)
  (26.03.05)
  
Nickel-Strunz
(10th edition) :
06.CB.10
  (06) Borates
  (06.C) Triborates
  (06.CB) Ino-triborates
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: P21/a
Unit cell: a =8.712(2))Å, b = 11.247(3)Å, c =6.091(1)Å; β = 110.12(2)° Z = 2
Crystal Habit: As equant to short prismatic crystals, with large {110} and multiple terminating forms, to 30 cm; pseudorhombohedral with large {110} and {301}; pseudo-octahedral with large {221} and {011}; nearly 50 forms measured; cleavable massive, granular, most commonly nodular.
  
Color: Colorless, milky white, pale yellow, gray; colorless in transmitted light
Diaphaneity: Transparent to translucent
Luster: Vitreous to adamantine
Hardness (Mohs): 4.5
Measured Density: 2.423(5) g/cm3
Cleavage: On {010}, perfect; on {001}, distinct
Fracture: Uneven to subconchoidal
  
Geologic Setting: A common constituent in borate deposits formed in arid alkaline lacustrine environments, deficient in sodium and carbonate, typically under warm conditions.
Mineral Association: Howlite, ulexite, searlesite, priceite, nobleite, ginorite, gowerite, luneburgite, kernite, gypsum, calcite, celestine
Ore deposits: A chief source of boron.
  
Luminescent Properties: Bright pale yellow fluorescence, may phosphoresce pale green;
Other Properties: Piezoelectric. Pyroelectric. Gemstone Extremely Rare.
Comments: Piezoelectric at very low temperature.

 

Colemanite
Colemanite (milky white) with realgar (reddish orange)
Origin: Boron, Inyo Co., California, USA.
Sample size: 8 x 5 x 4 cm
Photo: Tom Loomis

 

Colemanite
(zoom-in of above)

 

Colemanite
(another zoom-in of above)

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