Best viewed using Adobe Flash Player (8 or higher).
Download hereGENERAL DESCRIPTION
Topaz is a rare fluorinated and hydrated aluminosilicate, which can be a semi precious stone when gemmy. It is present in the granites, pegmatites and in the hydrothermal veins but also in certain differentiated volcanic rocks (rhyolites).
When it is well crystallized, it appears in the form of biterminated elongated prisms. The crystals can be important by reaching several tens of kg. They are often transparent or with varied colours: colourless, yellow pale with orange, blue, pink.
Some topazes are heated in order to modify the yellow colour pink (burned topaz). The natural blue colour is rare. The majority of the crystals of this colour are the result of an artificial irradiation (with neutrons) on colourless crystals. Blue topazes (natural or synthetic) can sometimes be confused with the beryl aquamarine. Topaz is sought by collectors, jewellers and the museums for its colours and the shape of its superb crystals.
It is infusible and insoluble in the acid, which confers a great inalterability to it. Most beautiful topazes are thus used in jewellery. Topaz is announced in many localities: orange imperial topaz used as gem is exploited in the area of Ouro-Preto in Brazil. In Zambia, close to Solwezy, a deposit of beautiful topazes of orange colour was discovered. In the district of Virgem da Lapa also in Brazil, it was discovered between 1976 and 1978 of beautiful blue topaz crystals measuring more than 25 cm. At the Alabaschka deposit in the Ural Mountains of Russia, blue snowy crystals of ten cm were found.
In France, topaz is present in some deposits: the mine of Montebras (Creuse), many mines of the surroundings of Ambazac, Bessines-on-Gartempe, Razès and of Saint-Sylvestre (Limousin), and the area of Echassières (including the Montmins mine, Allier) for the most known localities. We can also quote the Framont mine (Alsace), Montignat and Chaillat (Puy de Dôme), Montbelleux, La Villeder, Penestin, Sarzeau and Ambon (Brittany), Gilly-sur-Loire (Saone and Loire) and the Herbiers (Vendée) without forgetting the volcanic microtopazes near Villefranche de Rouergue (Aveyron).
The type is not definable because it acts of a described old species before the conditions of deposit of the types were not defined.
HISTORY : Name inspired from the Greek word [topazion] meaning searching. This name was given to the yellow cristals found on the Topasos (Zabargat) island in the Red Sea
Species described by Anselmus Boaetius de Boodt (1150-1632), Belgian naturalist
Type-locality : undefined because species already known from the Ancients
ANCIENT NAME : Alumine fluatée siliceuse
CHEMICAL FORMULA : Al2 SiO4 (F,OH)2
CRYSTAL SYSTEM : Orthorhombic
COLOR : Colorless, yellow, pink, orange, blue
DIAPHANIETY : Transparent to opaque
LUSTER : Vitreous
STREAK : White
MORPHOLOGIE : Well-formed crystals, prismatic
HARDNESS : 8
CHEMICAL CLASS: 3,5-3,6
DENSITY : VIII - Silicates
GROUP : Topaz
STRUNZ CLASS BEFORE 2001 : 8/B.02-70
STRUNZ CLASS AFTER 2001 : 9.AF.20
