Schorl or Schorlite

Tourmaline group - cyclosilicates

Formule chimique : NaFe2+Al6(BO3)3(Si6O18)(OH)4
Système cristallin : Rhombohedral
Etymologie : From the German Scorl.
Dureté : 7
Densité : 3.1 – 3.3
Propriétés physiques : Vitreous shatter, dark brown to black in colour. Indistinct cleavage.
Propriétés chimiques : Unaffected by acids.
Formule chimique : NaFe2+Al6(BO3)3(Si6O18)(OH)4
Habitus : In well-formed elongated prismatic crystals with striations in the elongation or in aggregates of small crystals.
Gîtologie : Schorl belongs to the tourmaline group. It is an accessory mineral of metamorphic rocks, leucogranites and pegmatites.
Determination : Easy because of its colour and habitus.
Utilisation : Due to its piezoelectric properties, tourmaline is used in electrochemistry. When it is a gem, it can be used in jewellery with its diversity of colours.

Schorl is typically found in pegmatites throughout the world. The most beautiful deposits are in Brazil (Minas Gerais), California and Madagascar.
In France, it is found in the pegmatites of the Massif Armoricain, the Massif Central and the Pyrenees. It forms a series with dravite.

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