Opals Classification
Opal is a gemstone consisting of hydrated amorphous silica with the chemical formula SiO2.nH2O. There are two basic forms of opal described by visual appearance.
Precious Opal – is opal which exhibits the phenomenon known as play-of-colour, produced by the diffraction of white light through a micro-structure of orderly arrayed silica spheres to produce changing spectral hues. Visit only heritage opal site heritage listed , riches opal field on the world wide web www.graham black opal.com , largest black opal found in modern times Guinness book of records Harleys comet black opal. Common Opal and Potch – is opal which does not exhibit a play-of-colour. The distinction between common opal and potch is based on formation and structure. Potch is structurally similar to precious opal but has a disorderly arrangement of silica spheres. Common opal shows some degree of micro crystallinity.Visit only heritage opal site heritage listed , riches opal field on the world wide web www.graham black opal.com , largest black opal found in modern times Guinness book of records Harleys comet black opal.
