Mineral Information and Data:

Gedrite
[]Mg5Al2(Si6Al2)O22(OH)2 [CNMNC approved formula]

Named for the locality: Heas Valley near Gedres, France. First published in 1836. Redefined per nomenclature of amphiboles (IMA, 1978).

IMA status : Redefined IMA Approved; 1978 ()
CLASSIFICATION 
Dana
(8th edition) :
66.01.02.06  
  (66) Inosilicate Double-Width Unbranched Chains, W=2
  (66.01) with P=2 amphibole configuration
  (66.01.02)
  
Nickel-Strunz
(10th edition) :
09.DE.05
  (09) Silicates
  (09.D) Inosilicates* Structural terminology per Liebau (1985)
  (09.DE) with 2-periodic double chains, Si4O11; Clinoamphiboles
  
Crystal system: Orthorhombic System
Point group (H-M): mmm (or 2/m 2/m 2/m) — dipyramidal
Space group: Pnma
Unit cell: a = 18.59Å, b = 17.89Å, c = 5.3Å, Z = 4
Crystal Habit: As bladed and prismatic crystals; fibrous and semi-sheaf-like aggregates.
  
Color: White, gray, brown, green; colorless, gray, or brown in thin section
Diaphaneity: Transparent to translucent
Luster: Vitreous
Hardness (Mohs): 5.5 - 6
Measured Density: 3.15 - 3.259 g/cm3
Cleavage: Perfect on {210}, intersecting at 54° and 126°, imperfect on {010}, {100}
Tenacity: Brittle
  
Polymorphism and Series: Forms a series with magnesio-gedrite and ferro-gedrite.
Geologic Setting: Widespread in medium- to high-grade metamorphic rocks; in metasomatized contact metamorphic rocks.
Mineral Association: Garnet, cordierite, "hornblende" anthophyllite, cummingtonite, sapphirine,
sillimanite, kyanite, quartz, staurolite, biotite.
  
Other Properties: Gemstone Unlikely Available.

 

Gedrite
Matrix with masses of small brownish gedrite throughout.
Origin: Moapa District, Clark Co., Nevada, U.S.A.
Sample size: 3.3 x 2.3 x 1.2 cm
Photo: Dan Weinrich

 

Gedrite
(zoom-in of above)

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