Opal

Opal is the most colorful of gems. Its splendid play of color is unsurpassed, and fine examples can even be more valuable than Diamond. The play of color consists of iridescent color flashes that change with the angle at which the stone is viewed. This phenomenon is often called opalescence. The play of color may consist of large, individual flashes of color (known as schillers), or may be of tiny, dense flashes. The intensity and distribution of the color flashes is a determining factor in the value of an Opal.

Chemical Formula	SiO2 · nH2O
Color	White, Colorless, Blue, Red, Green, Yellow, Orange, Brown, Pink, Purple, Gray, Black, Banded, Multicolored
Hardness	5.5Â -Â 6.5
Crystal System	Amorphous
Refractive Index	1.37Â -Â 1.47
SG	1.98Â -Â 2.25
Transparency	Transparent to translucent
Double Refraction	None
Luster	Vitreous, pearly, waxy
Cleavage	None
Mineral Class	Opal