Mineral Information and Data:

Dumortierite
(Al,[])Al6BSi3O16(O,OH)2 [CNMNC approved formula]

Named for Eugène Dumortier (1802-1873?), French paleontologist, of Lyons, France.

IMA status : Valid species (Pre-IMA 1881) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
54.01.02.01  
  (54) Nesosilicate Borosilicates and Some Beryllosilicates
  (54.01) with (BO3)
  (54.01.02) Dumortierite group
  
Nickel-Strunz
(10th edition) :
09.AJ.10
  (09) Silicates
  (09.A) Nesosilicates (Isolated tetrahedron) structures
  (09.AJ) Nesosilicates with BO3 triangles and/or B[4], Be[4] tetrahedra, cornersharing with SiO4
  
Crystal system: Orthorhombic System
Point group (H-M): mmm (or 2/m 2/m 2/m) — dipyramidal
Unit cell: a = 11.77Å, b = 20.21Å, c = 4.71Å
Crystal Habit: Crystals prismatic, rare; massive, columnar, fibrous or granular
Twinning: Common on {110}, which may produce trillings.
  
Color: Blue, violet, pinkish, brown
Diaphaneity: Transparent to translucent
Luster: Vitreous to dull
Hardness (Mohs): 8.5
Measured Density: 3.71 to 3.41 g/cm3
Cleavage: 2; {100} good, {110} imperfect
Streak: White
  
Geologic Setting: In aluminum-rich regionally metamorphosed rocks, disseminated and in veinlets cutting schists; also in pegmatitic veins.
Mineral Association: Quartz, cordierite, kyanite, andalusite, sillimanite, muscovite, rutile.
  
Other Properties: Gemstone Extremely Rare.

 

Dumortierite
This specimen has three divergent fans composed of acicular purple to lilac colored crystals to 2.3 cm in andalusite matrix
Origin: Dehesa, San Diego Co., California, United States
Sample size: small cabinet
Photo: Tom Loomis

 

Dumortierite
(zoom-in of above)

 

Dumortierite
This specimen of andalusite has exposed fan-shaped sprays of lavender coloured dumortierite. Under SW UV light the dumortierite fluoresces bluish violet. Dehesa is one of the very few localities that has fluorescent dumortierite.
Origin: Dehesa, San Diego County, California, U.S.A.
Sample size: 7.5 x 5 x 2.5 cm
Photo: John Veevaert, Trinity Mineral Co

 

Dumortierite
(zoom-in of above)

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