Opal takes its name from the Latin word Upala meaning precious stone. The Roman scholar Pliny described opal as ring having the fire of carbuncle (a deep red garnet) and the brilliance of amethyst with the green color of emerald. The Romans believed opal was the symbol of hope and purity. They called it cupid paederos (child as beautiful as love) and thought the wearer safe from disease.
For those who were born in the month of October the Opal is the traditional birthstone. The October birthstone poem reflects some of the properties with which the Opal is associated – hope, innocence and purity. The Traditional Metaphysical Properties for the October Birthstone Opal are happiness, faithfulness, loyalty and confidence. The healing properties of the October birthstone are reputed to be effective for health problems relating to the eyes and eye infections. The Opal is also used to enhance visualization, imagination, dreams and healing.
The Australian opal fields were at one time under the sea, so opalised fossils are occasionally unearthed. As the ages passed and the seas began to recede, millions of sea creatures were isolated and marooned. Eventually the area dried completely and the inland is now a dry desert country.
In time the ground waters, holding silica solution, also evaporated. They left behind the phenomenon known as ‘opal’. Hydrated silica was deposited in fissures in sandstone, or gypsum, and on jasper. It entered the shells of the stranded marine creatures. In some cases it even replaced the entire shell.
One can find opalised wood, prehistoric animal bones, sea creatures, full sea shells, skin shells, sponges, fish skeletons and even opalised stems of plants on the opal fields.
Boulder opal is classified as solid opal. It occurs as thin veins of precious opal in the cracks and cavities of light and dark brown ironstone boulders in Queensland, Australia. The opal flowed into the cracks and fissures in the boulders in liquid form millions of years ago. With the passing of centuries, the liquid material formed into solid opal and now miners cut these stones into magnificent pieces with the natural host rock left on the back.
Black opal is the most rare and valuable of all opal. It is solid and generally found as a bar (or bars) of various colours in a dark body (black, blue, brown or grey). Some black opals have a complete rainbow of colours while others have deep blue-green hues. Black Opal comes from the Lightning Ridge region of Northern New South Wales. It is the most rare and valuable opal. Fine quality black opals often cost more per carat than diamonds. The term black opal is misleading because the opal is not actually black, but instead has a very dark base. This dark base enhances the brilliant colors known as “fire”.
There are also semi-black opals and black crystal opals. While a true black opal displays sharp brilliant colours on a dark background, the semi-black opal shows a background or body colour of mid-grey. In contrast, the black crystal opal is translucent with no traces of black potch on it underside. Its colours are sharp and visible beneath the surface.