Mineral Information and Data:

Staurolite
Fe2+2Al9Si4O23(OH) [CNMNC approved formula]

Named from Greek "stauros", a cross, alluding to the cruciform twins it displays in some cases.

IMA status : Valid species (Pre-IMA 1792) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
52.02.03.01  
  (52) Nesosilicate Insular SiO4 Groups and O, OH, F, and H2O
  (52.02) with cations in [4] and >[4] coordination
  (52.02.03)
  
Nickel-Strunz
(10th edition) :
09.AF.30
  (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: Monoclinic System
Point group (H-M): 2/m — prismatic
Unit cell: a = 7.87 Å, b = 16.58 Å, c = 5.64 Å, b = 90.2°
Crystal Habit: Crystals short prismatic, rough surfaces
Twinning: Common on {031} or {231} as 90° or 60° cruciform penetration twins
  
Color: Dark brown, reddish brown, yellowish brown, brownish black
Diaphaneity: Translucent
Luster: Vitreous to resinous
Hardness (Mohs): 7 to 7.5
Measured Density: 3.65 to 3.83 g/cm3
Cleavage: 1; {010} distinct
Tenacity: Brittle
Fracture: Sub-conchoidal
Streak: White to grayish
  
Geologic Setting: Common in pelitic schists, gneisses, and argillaceous rocks regionally metamorphosed to amphibolite grade; also a detrital mineral.
A special property of staurolite is that it often occurs twinned in a characteristic cross-shape. In handsamples, macroscopically visible staurolite crystals are of prismatic shape. They are often larger than the surrounding minerals and are then called porphyroblasts.
Mineral Association: Almandine, sillimanite, kyanite, tourmaline, muscovite, quartz, chloritoid
  
Synonyms/varieties: Lusakite (Co-rich variety), Croisette, Fairy Stone
Other Properties: Gemstone Extremely Rare.

 

Staurolite
Penetration twin
Origin: Keivy, Kola Peninsula, Russia
ex. Ernie Schlichter Collection
Sample size: 7.5 x 6.5 x 2.5 cm
Photo: Rob Lavinsky

 

Staurolite
Plate of staurolite-garnet schist with 1-2 cm sized staurolite crystals
Origin: eastern valley-slope, east of Russånes, Norway
Sample size: 14 x 22 cm
Photo: Diederik Visser

 

Staurolite
Schist matrix with single and "fairy cross" twinned crystals
Origin: Picuris district, Taos Co., New Mexico, U.S.A.
Sample size: 12.6 x 11.2 x 4.2 cm
Photo: Dan Weinrich

 

Staurolite
(zoom-in of above)

<<< BACK TO MINERAL SEARCH