Glittering Stones >> Semi Precious Stones >> Opal

Semi Precious Stone Opal

The mineral opal is amorphous hydrated silica, its water content sometimes being as high as 30%. Being amorphous has no crystal form, occurring in its irregular veins and masses. It has concordat fracture, hardness 5.5-6.5, specific gravity 2.1-2.2, and a highly variable color. Opal ranges from colorless through white, milky blue, gray, red, yellow, green, and also brown and black. Often many of these colors could be seen at once, caused by interference from minute cracks in the opal which are normally filled with secondary silica and by thin lamellae formed inside the opal during its solidification. The term "opalescent" usually refers to this unusual and beautiful type of color.

Historical Facts Of Opal

Refractive Index: 1.44 - 1.46

Chemical Composition: SIO2nH2O

Hardness: 5.5 - 6.0

Density: 2.65 - 3.00

Crystal Group: Amorphous

Ocurrence: Czechoslovakia, Mexico, Honduras, Australia, Brazil, Tanzania

Types: Milk opal, Resin opal, Wood opal, Menilite, Hyalite, Glass-clear opal

Color information: White, Green, Blue, Black, Red, Orange, Violet, Pink, Grey, Yellow

Gemstone Opal Jewelry