Rock crystal from the Dauphiné region of France.
Transparent variety of the silica mineral quartz
that is valued for its clarity and total lack of colour or flaws. Rock crystal formerly was used extensively as a gemstone, but it has been replaced by glass and plastic; rhinestones originally were quartz pebbles found in the Rhine River. The optical properties of rock crystal led to its use in lenses and prisms; its piezoelectric properties (see piezoelectricity
) are used to control the oscillation of electrical circuits.
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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.