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Staurolite
Current inventory:  0 gems
 

Chemistry:  (Fe²⁺;Mg)₂Al₉(Si;Al)₄O₂₀(O;OH)₄
[Iron Aluminum Silicate Hydroxide]

Discovered in 1792;   IMA status: Valid (pre-IMA; Grandfathered).
Staurolite gets its name from the Greek words stauros and lithos, meaning stone cross.

Classification

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/B.03-10

Nickel-Strunz 10th Ed. ID:

9.GD.10

9 : SILICATES (Germanates)
A : Nesosilicates
F : Nesosilicates with additional anions; cations in [4], [5] and/or only [6] coordination

Related to:

Staurolite Group. Staurolite - Gerstmannite Series

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Commonly in prismatic crystals, typically rough, to 12 cm.

Twinning:

Commonly as 60º twins with [231] as twin plane, may be cyclic; less commonly as 90º cruciform twins with [031] as twin plane.

Physical Properties

Cleavage:

[010] Distinct

Fracture:

Conchoidal

Tenacity:

Brittle

Hardness (Mohs):

7.0 - 7.5

Density:

3.74 - 3.83 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Dark Reddish Brown to Blackish Brown, Yellowish Brown, rarely Blue

Transparency:

Transparent to Opaque

Luster:

Sub-Vitreous to Resinous

Refractive Index:

1.736 - 1.762  Biaxial ( + )

Birefringence:

0.0090 - 0.0150

Dispersion:

Weak; r > v

Pleochroism:

Visible; X = colorless, Y = pale yellow, Z = golden yellow

Occurances

Geological Setting:

Common in pelitic schists, gneisses, and argillaceous rocks regionally metamorphosed to amphibolite grade; also a detrital mineral.

Common Associations:

Almandine, Chloritoid, Kyanite, Muscovite, Quartz, Sillimanite, Tourmaline

Common Impurities:

Ti, Cr, Mn, Co, Zn, Li, H₂O

Type Locality:

n/a

Year Discovered:

1792

View mineral photos:

Staurolite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Staurolite is extremely rare as a faceted gem. The mineral forms in interesting crystals shaped like crosses or X's and are sometimes referred to as "Fairy Stone" or "Fairy Cross." Staurolite is famous for these "twinned" crystals that forms two twin types; one that is nearly 90 degrees (like a cross) and one that is nearly 60 degrees (like an X). The 60 degree type is more common but the 90 degree type is the most sought after as a symbol of the Christian cross and as a good luck charm. Some rare specimens show both twin forms together and look like a six rayed star. Transparent material is rarely found and cut gems are typically small and very dark red. They lack fire but are prized for their rarity.

Most facetable material comes from Ardenella and Rubellita, Minas Gerais, Brazil; Liaoning Province, China; and Pizzo Forno and Alpe Piona, Ticino, Switzerland.
 

  
Staurolite gems for sale:

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