SCHORL

    Class : Silicates
    Subclass : Cyclosilicates
    Crystal system : Trigonal
    Chemistry : NaFe3Al6(BO3)3Si6O18(O,F,OH)4
    Rarity : Very common


Schorl (or schorlite) is black tourmaline, the most common mineral of the tourmaline group. It is found mainly in granitic pegmatites, with quartz, feldspar and micas, but also in certain metamorphic rocks (often in relation to granitic intrusions), and in certain pneumatolytic deposits with tin or tungsten. Very resistant to alteration, it is also frequently found in alluvium. Its name is of uncertain origin and seems to derive from the German mining term "schurl", which designated small black stones, impurities rejected during the washing of gold and tin ores. Generally well crystallized, schorl forms elongated prisms that are strongly striated according to the elongation, sometimes of very large dimensions (up to 2 meters), with a triangular section with curved edges and pyramidal terminations. The crystals are also frequently acicular, grouped in felted aggregates or in parallel or radiate groupings. The crystals are often broken and cemented by later minerals (especially quartz). Schorl is black in color, translucent in brown in fine splinters. It is cut for jewelry.

Main photo : Schorl from Erongo Mountains, Usakos, Namibia

Schorl from Erongo Mountains, Usakos, Namibia
Schorl on quartz from Minas Gerais, Brazil
Schorl from Biauchaud, Puy-de-Dôme, France © Alain Tuel
34.00 ct schorl gemstone from India

Schorl in the World

Schorl deposits are very numerous. The Malagasy and American pegmatites (Maine) provide an abundance of large crystals. Particularly spectacular decimetric prisms (over 25 cm) are also known in California, associated with smoky quartz and albite (Ramona and Fano). Kragerö (Norway) is known for its 5 cm double-terminated crystals. Very good specimens of crystallized schorl have also been found in the pegmatites of the Gilgit region in Pakistan as well as Erongo (Namibia).

Schorl in France

In France, schorl crystals exceeding 10 cm are common in the pegmatites of the Armorican Massif (Saint-Pol-de-Léon, Saint-Jacut-de-la-mer...), Ariège and especially Lozère (La Chomette), where crystalline masses exceeding 100 kg have been found. Large crystals embedded in massive quartz are also known in the Biauchaud pegmatite (Puy-de-Dôme).

Twinning

Rare twinning is known on {10-10} and on {40-41}.

Fakes and treatments

No fakes listed for this mineral species.



Hardness : 7
Density : 3.18 to 3.22
Fracture : Irregular to sub-conchoidal
Streak : Gray-white


TP : Translucent to opaque
RI : 1.635 to 1.672
Birefringence : 0.025
Optical character : Uniaxial -
Pleochroism : Strong
Fluorescence : None


Solubility : Insoluble

Magnetism : ParamagneticRadioactivity : None