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Download hereGENERAL DESCRIPTION
Very widespread on the surface of the Earth, quartz is a silicon oxide which one names also silica. Quartz has many varieties defined by their colour (among most known: rock crystal which is limpid and transparent, the citrine one which is yellow-orange, the amethyst which is violet, the morion which is brown or black).
The microcristallized varieties name chalcedony. One will distinguish the red cornaline, the apple-green chrysoprase green and the brown jasper. The zoned varieties are the agates, onyx, the sardonyx (which used for cameos) and the jasper that has many different textures and color combinations.
Quartz is frequent in prismatic the crystal shape with faces striated and finished by triangular faces. Moreover, the conditions of growth can generate various morphologies: quartz known as "gwindel" is characterized by a preferential growth of its edges and its tops. Quartz "cathedral" a growth disturbed by foreign mineral inclusions and present had a disunited crystal aspect. "Sceptre" quartz has a crystalline overgrowth on a termination. Quartz "phantom" incorporated has one precise moment of its growth of solid inclusions, thus leaving a fingerprint of its growth inside the crystal.
Quartz is a common mineral present in eruptive, sedimentary and metamorphic rocks. It also can be found in pegmatites, sometimes of impressive size - and in the hydrothermal veins.
It is exploited as raw material in the manufacturing process of synthetic quartz. For a long time, it was cut and used as support of engraving. Many decorative and usual objects out of cut and engraved quartz, were added to the royal treasures. Being piezoelectric (polarizes electrically under the action of a mechanical constraint and, reciprocally, becomes deformed when an electric field is applied to them), it is also used in electronics and watch industry.
The quartz deposits are very numerous, but the sites offering of very beautiful quartz are definitely less abundant. It is necessary to quote the giant crystals discovered in Minas-Gerais in Brazil, these crystals measure several meters and weigh several hundred kilos. The site of Oberstein in Germany provided beautiful amethyst.
In France, the mine of Gardette (Isère) is probably the best known quartz deposit, quartz is associated with native gold there. This mine gave its name to one of the twins of quartz ("Dauphiné").
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 from "quarz", old german word "querch" meaning dwarf
Species known since Prehistory
Type-locality: undefined because species already known from the Ancients
CHEMICAL FORMULA : SiO2
CRYSTAL SYSTEM : Rhomboedric
COLOR : Colorless, white, pink, violett, black, yellow
DIAPHANIETY : Transparent to opaque
LUSTER : Vitreous to greasy
STREAK : White
MORPHOLOGIE : Prismatic crystals, massive, forming aggregates
HARDNESS : 7
CHEMICAL CLASS: 2,66
DENSITY : IV - Oxides and hydroxides
GROUP : Quartz
STRUNZ CLASS BEFORE 2001 : 4/D.01-10
STRUNZ CLASS AFTER 2001 : 4.DA.05
