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Chemical Formula: SiO2nH2O
Mineral Name: Opal
Color: Opaque to translucent white with green, blue, yellow, orange, red crystals
Hardness: 5.5- 6.5
Specific Gravity: 1.98 - 2.20

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Opal is a mineral of hydrated silica. They are luminous and iridescent with inclusions of many colors. Opal is a mineral composed of noncrystalline (amorphous) silica (and some water) and is a species of quartz. It derives its name from the Sanskrit name for precious stone; upala.The various varieties of opals are: common opal, opalescent precious opal (white or black, with a rainbow-like iridescence caused by tiny crystals of cristobalite), and fire opal (a milky stone that is firey orange to red in color with no opalescence).

Opals show a play-of-color (a shifting of spectral colors) when the spheres are uniform size and arranged in regular 3-dimensional layers. The range of colors is determined by the size of the spheres. The brighter and more distinctive the play-of-color, the better the opal.

Opals are found in the regions of Mexico, Brazil, USA, Japan, Honduras, Kenya, Czechoslovakia, Peru, Canada and finally Australia that has huge varieties of attractive opals.