Opal - Precious, Fire, Common Opal

Opal consists of silica and water. The amount of water varies in different specimens.
Opal is divided into three subgroups: Precious Opal,  yellow-red Fire Opal and Common Opal. Their physical properties vary considerably. Precious Opal is conspicuous amongst all others for the magnificent play of colors produced by the refraction and reflection of light in its colorless substance.