Mineral Information and Data:

Sillimanite
Al2OSiO4 [CNMNC approved formula]

Named after Benjamin Silliman (1779-1864), Professor of Chemistry and Geology, Yale University, New Haven, Connecticut, USA, and founder of the American Journal of Science (Silliman.

IMA status : Valid species (Pre-IMA 1824) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
52.02.02a.01  
  (52) Nesosilicate Insular SiO4 Groups and O, OH, F, and H2O
  (52.02) with cations in [4] and >[4] coordination
  (52.02.02a) Al2SiO5 (Sillimanite subgroup)
  
Nickel-Strunz
(10th edition) :
09.AF.05
  (09) Silicates
  (09.A) Nesosilicates (Isolated tetrahedron) structures
  (09.AF) Nesosilicates with additional anions; cations in [4], [5] and/or only [6] coordination
  
Crystal system: Orthorhombic System
Point group (H-M): mmm (or 2/m 2/m 2/m) — dipyramidal
Unit cell: a = 7.470 Å, b = 7.663 Å, c = 5.759 Å
Crystal Habit: Crystals long prismatic, vertically striated, nearly square cross section, massive, fibrous to somewhat columnar
  
Color: Colorless, white, gray, yellowish, brownish, greenish bluish
Diaphaneity: Transparent, Translucent
Luster: Vitreous to silky
Hardness (Mohs): 6.5 to 7.5
Measured Density: 3.23 to 3.27 g/cm3
Cleavage: 1; {010} perfect
Tenacity: Tough in aggregate
Fracture: Uneven
Streak: White
  
Polymorphism and Series: Trimorphous with kyanite and andalusite
Geologic Setting: In high-grade metamorphic schists, gneisses, and hornfels; more rarely in pegmatites. Also as a detrital mineral.
Mineral Association: Andalusite, kyanite, potassic feldspar, almandine, cordierite, biotite, quartz
  
Synonyms/varieties: Selmanite, Fibrolite, Monrolite
Other Properties: Gemstone Rare.

 

Sillimanite
Origin: Ratnapura, Hakurutale, Sri Lanka
Sample size: 1.2 x 0.7 x 0.25 cm
Photo: Rob Lavinsky

 

Sillimanite
Origin: Orissa, India
Sample size: 2.7 x 2.1 x 0.9 cm
Photo: Rob Lavinsky

 

Sillimanite
(zoom-in of above)

 

Sillimanite
Typical almandine-sillimanite-biotite gneiss from this high-grade metamorphic granulite facies region;
Garnet is present as anhedral lensoid aggregates
Origin: Gyadal, Rogaland, Norway
Sample size: 5 x 7 x 9 cm
Photo: Diederik Visser

<<< BACK TO MINERAL SEARCH