Staurolite | Gemopedia

The name staurolite comes from the Greek word stauros, meaning cross. Staurolite is prized for its twinned crystals that intersect at 60 or 90 angles forming x-like or perpendicular crosses and specimens exhibiting these forms are highly prized by collectors. Sometimes referred to respectively as St. Andrew's and Greek crosses as well as lucky cross, fairy stone or fairy cross, one legend says the crystal crosses were created by the tears of fairies whom could not help but cry when they heard of Christ's crucifixion. Staurolite is a metamorphic mineral that ranges from translucent to opaque in appearance and facetable gems are vary rare.
Colors
Reddish Brown, Blackish Brown, Yellowish Brown, Rarely Blue

Staurolite Classification

Common Name

Staurolite

Species

Staurolite

Variety

Facet Grade Staurolite

Colors

Reddish Brown, Blackish Brown, Yellowish Brown, Rarely Blue

Alternate Names

Gemstone Groups

Key Separations

Appearance of twins, RI and birefringence

Comments

Twinned crystals are 90o or 60o from each other.

Staurolite Optical Properties

Transparency

Transparent - Translucent

Refractive Index

1.736-1.746
Tolerance:(+0.015/-0.015)

Birefringence

0.009-0.015

Optic Character

Biaxial

Optic Sign

Positive

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

Trichroic, moderate yellow to red, brownish yellow, and colorless

Dispersion

Strength: moderate fire Value: 0.021

Comments

Staurolite Chemistry & Crystallography

Chemical Name

iron aluminum silicate hydroxide

Chemical Formula

(Fe,Mg,Zn)2Al9(Si,Al)4O22(OH)2

Synthesis

Crystal System

Monoclinic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Comments

Staurolite Characteristic Physical Properties

Hardness

7-7.5

Streak

White

Specific Gravity

3.65-3.79 Typical:3.71

Toughness

Fair

Inclusions

Luster

Vitreous

Stability

Fracture

Conchoidal, Uneven

Cleavage

Good, in one direction

Comments

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