Types of Opal Primary Terms Black opal, precious opal with black body color. Also used for black potch covered with thin layer of crystal opal that lets the black under layer show through. Semiblack, or gray opal, precious opal with dark body color. White opal, precious opal with white or very light body color. Crystal opal, transparent to semitransparent, colorless body with play of color. Doublets and Triplets make use of opal that is too thin to use as a solid gemstone. A doublet is a thin layer of precious opal glued to a black base. A triplet adds a transparent, quartz cap. … Purists prefer the base material to be common opal. However many black materials are used, including old phonograph records . Black crystal opal, transparent to semitransparent opal, with dark body color and play of color. Fire opal, translucent to transparent, with yellow, orange, or red body color. May or may not have play of color. Also called Mexican opal or Sun opal. Boulder opal, a thin seam of precious opal on ironstone matrix. Since this is a natural occurrence, its value is higher than that of a man made doublet. The ironstone is very dark, which makes the fire stand out and gives a close resemblance to black opal. Matrix opal consists of thin seams or spots of precious opal in matrix. The matrix is usually dark ironstone, but occasionally a light sand stone. Also called Mass opal.
Types of Opal Primary Terms .
Black opal, precious opal with black body color. Also used for black potch covered with thin layer of crystal opal that lets the black under layer show through.
Black Opal. A Black Opal is so named because of its natural dark base colour which can be black, dark blue or dark gray. The surface colours can range from a variety of blues and greens to all the brilliant colours of the rainbow. It is found in two centres of Australia—Lightning Ridge in New South Wales and Mintabie in South Australia. The Lightning Ridge Opal is the better of the two, due to brilliance and intensity of colour. The Lightning Ridge Black Opal is the most expensive of all the opal types, on a dollars per carat basis, due to its absolute rarity and the demand from collecters around the world.
White Opal. The White Opal has a whitish base colour all over the gemstone. The brilliant colours emanate from this white base. One of the differences between White Opal and Black and Boulder Opal is the colour play generally extends from surface to base, or from skin to skin, whereas the other two types have a naturally occuring single base colour, differing from its surface colours.With a light texture base, this material can appear from a superior crystal gel form emerging with interplay of different firy bright colours down to a purely white milky solid. It is usually drawn from the mines in Coober Pedy, Andamooka in South Australia.
Boulder Opal. Found only in Queensland, this rare Opal was formed from silicon diozide and other minerals finding their way into the fissures of ironstone. The cutter must always take a little of this natural ironstone when extracting a gemstone and this gives the dark overall colour which does not detract from the Boulder Opal. When little or no ironstone appears in the face of Boulder Opal, the price of Boulder equals that of very fine Black Opals. The natural occurrence of Boulder allows for particularly interesting shapes which in the hands of a creative jeweller makes for stunning creations.
Triplet / Triplex. It is a three part piece consisting of the base (either vitrolite, plastic or obsidian), a centre slice of White Opal which has been painted black on the underside to give a Black Opal “look alike” appearance and has a top of Quartz as a protection for the thin layer of Opal (which is usually sliced to only 1000th of an inch).
Doublet Opal. Same as a triplet, but no quartz top. The Opal slice is usually rounded a little for a cabachon effect. It is made by gluing slices of precious opal to a common opal backing with blackened cement, usually an epoxy resin. The dark backing enhances the colours of the opal. Boulder Opal Doublet comprises of a layer of white opal on the top and attached by another layer of iron-backing stone from Boulder Opal underneath.
Matrix. There are two types of Matrix, one is known as Andamooka Matrix which is sugar and acid treated, Opal bearing rock, and the other is Queensland Boulder Matrix. Queensland Boulder Matrix is natural, but is not included in this collection except for a few bead items. It is simply naturally-occuring Opal and ironstone in a pepper and salt pattern.
Matrix opal consists of thin seams or spots of precious opal in matrix. The matrix is usually dark ironstone, but occasionally a light sand stone. Also called Mass opal. Opal also shows one of the best spectral displays of any gemstone, hence its value. It is made up of layers of precipitated silica spheres in a jelly-like water mass, and the ordering of the spheres sometimes produce a diffraction grating, that creates a play of rainbow sparkling light from within the stone.
There are fundamentally three types of opal: precious opal (containing flashes of fire), the yellow-reddish “fire opal” which is named for its color (not flashes of fire), and common opal (sometimes called “potch”).
“Common opal” is rarely transparent, but may be colored or contain inclusions. It is used as backing for the more desirable varieties of precious opal, but may also be cabbed to produce interesting stones. It comes in white, gray, yellow, blue, green, pink, and may be dendritic or contain moss.
“fire opal” is named for its fiery red color, and not the flashes from within. Today most fire opal comes from Mexico and is often cut into faceted gem stones. It runs from a deep red to many shades of orange and even on to yellow. It may have a few flashes of fire, but usually it is sold for the color and clarity. It is not particularly expensive as it suffers from the same physical characteristics as all opal, and contains little of the desired color flash.
“Precious Opal” – this is the material with the internal “color play”, “flash”, or “light show”. It is classified by its back ground color, the particular colors and intensity of color display, and its size. Stones that are predominantly white or light blue are the most common, and those that contain reds, oranges, and violets are considered more desirable. Blue and green are very common in most precious opal. Black opal, opal containing a predominantly dark background (dark-gray to blue-black) is the rarest, and most desired of all opals. When it contains reds and oranges it brings even a higher value. It may be priced right up with the top gemstones (diamond, emerald, and ruby). The very best black opal came from Lightening Ridge. Australia and small amounts till reach the market today, but there have been no major finds in many years.
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