Mineral Information and Data:

Chromdravite
NaMg3Cr6(BO3)3Si6O18(OH)4 [CNMNC approved formula]

Named for CHROMium in the composition and similarity to dravite.

IMA status : Approved Species 1983 (IMA1982-055)
CLASSIFICATION 
Dana
(8th edition) :
61.03e.01.11  (This Dana# Changed)
  (61) Cyclosilicate Six-Membered Rings
  (61.03e) with borate groups (Sodic Tourmaline Subgroup)
  (61.03e.01) Schorl Subgroup
  
Nickel-Strunz
(10th edition) :
09.CK.05
  (09) Silicates
  (09.C) Cyclosilicates
  (09.CK) [Si6O18]12- branched 6-membered single rings, with insular complex anions
  
Crystal system: Trigonal System
Point group (H-M): 3m — ditrigonal-pyramidal
Unit cell: a = 16.11Å, c = 7.27Å
Crystal Habit: In pyramidal acicular crystals, to 0.1 mm.
  
Color: Dark green to nearly black
Diaphaneity: Semi-transparent.
Luster: Vitreous, Resinous
Hardness (Mohs): 7 - 7.5
Measured Density: 3.40 g/cm3
Streak: Grayish-green.
  
Geologic Setting: In micaceous metasomatic clay-carbonate rocks
Mineral Association: Chromian phengite, taeniolite, vanadian muscovite, quartz, dolomite
  
Other Properties: Gemstone Rare.
Comments: The Cr3+ analogue of Dravite.

 

Chromdravite
Chromian dravite
Origin: Pein Pyet, Mogok, Mandalay Division, Myanmar
Sample size: 1.2 x 1.0 x 0.3 cm
Photo: Rob Lavinsky

 

Chromdravite
Chromium dravite
Origin: John Saul Ruby Mine, Mangari, Kenya
Sample size: 9 x 7 x 4 cm
Photo: Rob Lavinsky

 

Chromdravite
(zoom-in of above)

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