Opal Formation

Opal was formed in the Cretaceous period 65 to 140 million years ago, during the age of the dinosaurs. A large Inland Sea called the Eromanga Sea covered a large proportion of Australia. This was the start of this beautiful Australian National Gemstone. Opal!During this period of extreme weather conditions when the climate was wet and warm, a complex chemical alteration occurred in the rocks and minerals. The volcanic activity of this time also had a part to play in the development of opal.

Opal is formed from layers of minute silica spheres that are uniformly layered. Between these spheres, silica gel in solution is contained. Light is diffracted on the stone passing through the solution resulting in the beautiful rainbow colours of the opal.The resultant colours are in accordance to the size of the silica spheres and how closely packed they are. For example the smaller spheres create the blue, which is more common, and the larger spheres create the rarer orange and red opal, this rarity is reflected in the price.The forming of the opal occurs when the silica in solution seeps through cracks and fissures in the rock formation. The silica settles and over millions of years forms a hard gel, creating the finished opal gemstone.It is estimated it can take up to 5 million years for just 1 millimeter of opal to form. Opalised dinosaur fossils have been found uniquely in Australia, sometimes inside organic material (for example wood, foliage or dinosaur bones) encasing the already historical and intriguing bones in the eternal beauty of the opal.