Opal cat's eyes are also known from Brazil: Colours range from yellow to orange but occasionally reddish orange gems are found which match fine Mexican fire opals. The matrix is a light to dark brown ironstone containing pockets of precious opal.īrazil produces fire opals, sometimes of amazing sizes. Mexico is famous for fire opals, with, as well as without play of colour, and for matrix opals. The Yowah opal field in Queens produces boulder opals and Coober Peedy in South Australia is known for milk opals and crystal opals. Lightning Ride in New South Wales is the origin of the famous and highly priced black opal. The most important source for precious opal is Australia. However, most localities produce common opal only. Localities: opal is found on all continents including Antarctica. Some glasses, notably opal glass and Slocum glass, show opal-like colours and opalescence. A subsequent treatment with sulphuric acid turns the sugar into black carbon. This is often colour enhanced to imitate black opal. In Andamooka, South Australia, a porous rock with inclusions of precious opal is found. Precious opals can be confused with synthetic opal. There are yellow and brown honey opals which resemble amber, agate opals which show an agate-like banding and moss opals with dendritic inclusions very similar to moss agate, to name just a few. Mostly glass or plastic are used for the top, occasionally rock crystal is used.Ĭan be confused with: common opal without play of colour comes in many colours and patterns and may be confused with with a lot of other minerals. In a triplet this ensemble is covered by a protecting top of transparent material. In a doublet the opal layer is glued onto a, mostly black, base of onyx or plastic. Opal layers which are too thin to cut a gemstone but too good to be discarded are made into doublets and triplets. The stone on the left developed a crack and was thus worked into a doublet on onyxīlack opal from Lightning Ridge, Australia Mexican black obpal, found in the 1980ies To name a few: black opal, milky opal, crystal opal, boulder opal, matrix opal, harlequin opal, pinfire opal and many more Synonyms and trade names: opal has a plethora of trade names referring to body colour, play of colour, inclusions (moss opal) or origin. The origin of both these words most probably is the Sanskrit upala. Origin of name: derived from the Latin word opalus or the Greek ὀπάλλιος opallios meaning "precious stone". Mexican fire opal with and without play of colour The gem and jewellery trade knows three kinds of opal: precious opal (with play of colour), common opal (without play of colour) and fire opal (which comes both with and without play of colour). Transparent and translucent opals appear orange in transmitted light and bluish when viewed perpendicularly to the transmitted light. Opal contains up to 20% of water which may give rise to serious problems (see below: Worth knowing). If these spheres are present in more or less the same size and in the right arrangement, diffraction and interference of light can produce the famous play of colour. It consists of numerous tiny silica spheres. Opal is one of the very few amorphous minerals, which means that it has no crystal structure.Īpart from being amorphous, opal has some more specific features. Common mineral of the oxides and hydroxides class.
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