Opal is a quite soft stone which consists of silica gel usual manner 5-10% water.
Opal can dry and crack.
One rates opal in two varieties: Precious Opal and common opal.
Precious opal have a beautiful play of color while the ordinary opal is almost without shimmer and usually opaque.
Precious opal gets its beautiful color shimmer out of silica spheres it contains.
The larger the spheres, the greater color variation.
Since about 200 years so has Australia has been an important part out of the opal industry,
but also in. Africa, Mexico and the United States.
One can find opal in sedimentary rocks and can form stalagmites and stalactites.
Crystal structure: Amorphous
Composition: silica Silica Water
Refractive index: 1.37 to 1.47