Opals - Fire and Beauty: What to Look Out for When Buying Opal Jewellery The majority of quality opal stones are mined in Australia. Opals are formed from liquid silica which flowed into a gap or cavity and cooled, thus resulting in some very unusual shapes, such as wood, seashells and even dinosaur bones! This also means that opals have comparatively high water content, around 10%. For this reason they should never be allowed to dry out. Be especially careful with central heating radiators, or direct sun. I find it's best to keep them in a jewellery box or case when not being worn. Detergents can also affect them so don't do the washing up while wearing them! Not all opal is gem quality however, but the ones that are often need to be treated in order to make them more attractive and also to protect them from drying out. Opal stones can be manmade (either synthesized or altered in some way) and thus one can find many types of opal which are artificially produced...