The name opal comes from the Greek word opallios which means “to see a change of color”. According to Greek mythology, when Zeus defeated the Titans, the Greek god of lightning was so content that his tears of joy formed the gemstone opal.
Opals have a water content ranging up to 30%. This water content is responsible for opal’s signature feature, the play of color. If this water content were to decrease or diminish, opal would crack and the interplay of colors would disappear. A great number of studies have tried to find out the reason behind this phenomenon. In 1960's scientists have discovered the reason behind it. They have determined that opals were composed of small silica spheres formed in an organized manner, and they put an end to the question which echoed throughout history.
Australian Aborigines believed that opal was the footprint of the creator. Currently, Australia is the country which produces almost 95% of all the world’s opals. Most of this opal is located in Coober Pedy in South Australia.
Opal has a hardness rating of 5.5 to 6.5 on the Mohs scale, which makes them very brittle gems. They are very sensitive to light, so they should not be kept under direct sunlight. They should not come into contact with oil or cleaning products. Among all the gemstones, opal is easily the one that calls for the most care. Since contact with heat would evaporate the internal water, processing them calls for great care. Opals are also sensitive to pressure and impacts which is why safeguarding them in a humid cotton fabric is crucial for them to not get damaged.
While there is no globally accepted amethyst grading system, they may be classified according to their external and internal features, mainly their color, and clarity.
Opals in this category are the most common ones as they make up for 60% of all the opals earth has to offer. Decent quality opals do not show a play-of-color like the high-quality opals, and they have blemishes on their surface. In appearance, they are cloudy and opaque.
Around 30% of opals are in this category. Superior quality opals are cloudy, opaque and they have mild blemishes on the surface. Opals in this category show a little play-of-color, not as much as higher quality opals though.
Opals in this category are considerably rare as they make up for 10% of natural opals. Finest quality opals exhibit a moderate play-of-color, and only have very small blemishes on their surfaces. Similar to other opals, they are opaque in appearance.
Only a mere 1% of all the opal gemstone qualify to be in this category. Prodigious opals show an exceptional play-of-color. They have a cloudy appearance and do not have blemishes on their surfaces.