| Descriptions |
Opal hydrous silicon dioxide is a noncrystalline form of quartz containing up to 30 percent water. There are many types of opal. The name Opal comes from the Sanskrit upala meaning “valuable stone.” The common opal is milky white but opals can run the gamut from greenishyellow to brick red. There are some special varieties such as the fire opal of Mexico with rich reds and purples and the black opal of Australia but there are many others besides. Some are cachalong common potch boulder girasol harlequin hyalite hydrophane ironstone liver moss peacock wood white and water. Unlike other opals common or potch opal is a colorless opal produced by spheres which are not stacked orderly. Other opals have orderly stacked spheres which produce the play of colors characteristic of opals.
Some attempts have been made to synthesize opal but no attempt has been wholly successful. The Slocum stone created by John Slocum was one such attempt which while attractive is nothing like opal. Pierce Gilson also produced an imitation in the 70s but it is similar it is not similar enough to fool someone familiar with opals. White opals of a lesser quality are sometimes turned into black opals by the same sugaracid treatment which can turn chalcedony into black onyx. Another treated opal may be the “potch” opal which may be “impregnated” with plastic to give it a better show of colors. Another common practice is to make a composite stone of several opals with a backing of Opalite a black glass produced in Belgium making a gem less prone to crazing and cracking because it is held together by cement. Even if the opal is not doctored it may be covered in a glaze of transparent quartz to protect it from bumps and scratches.
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