Opal stone

Opal stone

Opal, as a gemstone, is a hydrate of silicon dioxide with a chemical composition of SiO2 · nH2O. It has an amorphous structure and therefore does not have a specific shape. Its fracture surface is shell like, mainly formed by the colloidal precipitation of silicon dioxide. In mineralogy, it belongs to the opal class and contains two types of gemstones: variable color and invariant color. It is a hydrated amorphous silica.