Opal
Opal is a mineral, a hydrogel with a fluctuating water content, whose chemical formula is SiO2-nH2O. The water content is most often between one and three percent by weight, but in some cases it can be as high as 20%. There are many varieties of opal in the world, such as precious opal, fire opal, wood opal and bush opal.
It is an amorphous silicate, which means it does not have a crystalline structure. Its colour changes depending on the angle of view and lighting, which gives it a special charm. Opal is often carved into different shapes and used to make jewellery such as necklaces, bracelets, rings and earrings.
