Opal is the most colorful of all gems. It is a form of silica chemically similar to quartz, but more like glass and containing a variable amount of water within the mineral structure. Its splendid play of color is unsurpassed, and fine examples can be more valuable than diamond. Precious opals (black and white) are cut and polished into cabochons and used in all forms of jewelry.
Color: White, green, blue, black, red, orange, violet, pink, grey, yellow.
Categories: precious stone
Chemical Composition: SIO2nH2O
Crystal Group: Amorphous
Refractive Index: 1.44-1.46
Hardness: 5.5 – 6.0
Density: 2.65 – 3.00
Occurrence: Czechoslovakia, Mexico, Honduras, Australia, Brazil, Tanzania.