Prehnite

Ino-Phyllosilicates

Formule chimique : Ca2Al(AlSi3O10)(OH)2 + traces of trivalent iron
Système cristallin : Orthorhombic
Etymologie : Dedicated to the Dutch colonel Hendrik von Prehn (1733-1785) who discovered this mineral.
Dureté : 6 – 6.5
Densité : 2.80 – 2.95
Propriétés physiques : Transparent to translucent. Colour yellow, grey, white, colourless, green and sometimes pink. Vitreous to pearly lustre. Irregular fracture, easy cleavage (001).
Propriétés chimiques : Almost insoluble in acids.
Formule chimique : Ca2Al(AlSi3O10)(OH)2 + traces of trivalent iron
Habitus : Often in botryoidal masses and aggregates. Rarely in automorphic crystals.
Gîtologie : Prehnite is a secondary hydrothermal mineral of basic rocks and crystalline schists.
Determination : because of its habitus and colour.
Utilisation : When it is of gem quality, prehnite can be used in jewellery.

The main deposits of beautiful prehnite are located in the USA (New Jersey), Scotland (Barrhead), India (Poonah), Namibia, Mali and Morocco.
In France, prehnite can be found at Bourg de la Selle in Isère.

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