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Schorl  (Black variety of Tourmaline)
Current inventory:  0 gems
 

Chemistry:  NaFe³⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
[Sodium Iron Aluminum Boro-silicate Hydroxide]

Discovered prior to 1400;   IMA status: Valid (pre-IMA; Grandfathered).
The name Schorl may have come from the Old German SchÄurl or Schürl, of uncertain derivation, perhaps meaning impurities. See below for more name information.

Classification

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/E.19-50

Nickel-Strunz 10th Ed. ID:

9.CK.05

9 : SILICATES (Germanates)
C : Cyclosilicates
K : [Si₆O₁₈]₁₂- 6-membered single rings, with insular complex anions

Related to:

Tourmaline Group. Elbaite - Schorl Series. Dravite - Schorl Series.

Crystal Data

Crystallography:

Trigonal - Ditrigonal Pyramidal

Crystal Habit:

Crystals prismatic to acicular, or may be flattened along [0001], with prominent trigonal prism and pyramid, to 1.5 m. Commonly hemimorphic, and striated [0001]. Also radial, fibrous, and massive.

Twinning:

Rarely on [1010], [4041].

Physical Properties

Cleavage:

[1120] very Poor, [1011] very Poor

Fracture:

Uneven to Conchoidal

Tenacity:

Brittle

Hardness (Mohs):

7.0

Density:

3.18 - 3.22 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Other:

Piezoelectric and Pyroelectric

Optical Properties

Color:

Black, Brownish Black, Greenish Black, Bluish Black

Transparency:

Opaque

Luster:

Vitreous to Resinous

Refractive Index:

1.635 - 1.672  Uniaxial ( - ); under strain may show slight Biaxiality

Birefringence:

0.0270 - 0.0320

Dispersion:

0.017

Pleochroism:

Very strong; O = yellow-brown; E = pale yellow, pale brown

Occurances

Geological Setting:

In granites and granite pegmatites, high-temperature hydrothermal veins, and some metamorphic rocks; also detrital.

Common Associations:

Albite, Beryl, Cassiterite, Epidote, Fluorite, Garnet, Microcline, Muscovite, Orthoclase, Quartz, Scheelite, Topaz

Common Impurities:

Mn, Mg, Ca, Li, Cr, Ti, F, K

Type Locality:

Possibly Zschorlau (Schürl), Saxony, Germany

Year Discovered:

prior to 1400 AD

View mineral photos:

Schorl Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

  
Schorl is the black variety of Tourmaline. It is colored black by the presence of iron. Schorl may also be dark bluish black and dark greenish black. Schorl is the most common mineral in the Tourmaline Group that also includes Buergerite, Dravite, Elbaite and Uvite. All Tourmalines form similar crystals because they are isostructural, meaning they share the same internal crystalline structure.

In addition to being found as independent mineral crystals, Schorl is also found as long thin crystal inclusions in Quartz, forming "Tourmalinated Quartz". These black crystals, or "needles", create very attractive and collectable Quartz gems.

The name Schorl may be derived from Zschorlau, the name of a village in Saxony, Germany which was named Schorl, or Schürl, prior to 1400 AD. The name may have come from the Old German SchÄurl or Schürl, of uncertain derivation, perhaps meaning impurities because Black Tourmaline was abundant in a nearby tin mine which also contained Cassiterite.

The name Tourmaline is from the Singhalese word tourmali, meaning mixed colored stones because Tourmalines were often confused with other gems because of the variety of colors. Tourmaline is the name given to a family of related minerals, all having the same basic crystal structure but varying widely in chemical composition. Tourmaline comes in just about all colors including colorless (Achroite) and black (Schorl) with many names given to the many other colors.
 

  
Schorl gems for sale:

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