The production of the brilliant colours in precious opal is made from the arrangement of silica spheres in a regular pattern, creating diffraction and interference of light rays.
One piece of precious gem opal usually cut en cabochon or free form. Highly appreciated by investors. Solid precious gem opal shows various degrees of transparency and also background colours.
Andamooka crystal opal being the rarest and most valuable of all Australian
opal. Queen Elizabeth II on her visit to Australia in 1954 was presented with
earrings and necklace with Andamooka crystal opal.
Doublet / Triplet
A thin slice of colourful opal is sandwiched between a clear domed capping of crystal quartz and a layer of black glass or potch. A doublet is similar to the triplet but without the protection of the quartz capping.
Andamooka Matrix Opal
Is a rare form of opal found only in the Andamooka opal fields in South Australia. Being a porous opal rock, its background colour can be darkened to black to enhance the beauty and brilliance of the gem colours and patterns. It is truly unlike any other opal. Andamooka Rainbow matrix is similar to Matrix Opal with a laquer.
This type of opal is highly appreciated by investors and collectors because of its rarity and beauty. It is produced by silica solution substituting the host bones or shells over a period of millions of years. The original form (eg clam shell, belemnite, bone) must be retained through polishing.
Boulder opal is gem-coloured opal found within a body of ironstone or iron-laden sandstone. It is named for the boulder-shaped lumps of ironstone in which it is often found. The gem colour usually occurs in thin, wavy sheets, so boulder opal is often cut with rock matrix on the back of the stone. Black opal is precious opal with gem colour on a natural black background.
Potch or Common opal is opal that does not contain gem colours. Common opal has the same chemical composition as gem opal; but whereas gem opal contains microscopic spheres arranged in a regular array, in common opal the arrangement of spheres is irregular. The best-known kind of common opal is potch, which may be black, grey, white or amber-coloured.
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