What is Opal?

Opal is a mineral that belongs to a large group of minerals known as the “Silica family”. Silica, known by its chemical formula as “SiO2”, is a mineral compound of two atoms; Silicon and Oxygen. The most common forms of Silica in our environment are crystals of Quartz, or sand, and also window glass. Opal is unique however as it also has in its formula a component of water or ‘H2O’. The complete formula for opal is SiO2,nH2O. When we look at the letter ‘n’ in the formula it relates to “how much” water is in the Opal.

Another special feature of Opal is how it’s structure is described, being “amorphous” or without form. This is from a mineralogical and atomic point of view. Quartz for example has a crystalline structure which goes deep down into its arrangement of atoms. Opal on the other hand does not have this regular structure at an atomic level. There are however various part’s that make up the composition of an Opal.

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