Olivine (or Peridot)

Silicate group - Mesosilicates

Formule chimique : (Fe,Mg)2[SiO4]
Système cristallin : Orthorhombic
Etymologie : The name olivine comes from its olive green colour.
Dureté : 7
Densité : 3.2 – 3.6
Propriétés physiques : Glassy sheen. Yellow-green to olive-green colour. Transparent to translucent. Conchoidal fracture. Imperfect cleavage in two directions (010) and (100)
Propriétés chimiques : Peridot is soluble in hydrochloric acid.
Formule chimique : (Fe,Mg)2[SiO4]
Habitus : Olivine is often found in rounded crystals and granular aggregates.
Gîtologie : Olivine (or peridot) is found as isolated grains in some basaltic lavas (basic volcanic rocks) or in aggregates with pyroxene in peridotites (ultrabasic rocks). Olivine is also found in some calcic metamorphic rocks and meteorites.
Determination : Easy because of the characteristic green colour and the habitus.
Utilisation : Magnesian olivine (called forsterite) is used as a refractory material. When it is of gem quality, olivine is used in jewellery under the name of peridot.

In the world, olivine crystals come from Austria (Kraubath), Germany (Fortsberg and Mosenberg), Birmaine, USA (Arizona and Hawaii).
In France, peridot is found in the basic volcanic rocks of the Chaîne des Puys and in peridotite nodules.

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