Light Opal has white or light appearance. It has a light or pale background and often displays red, green and blue pinfire. This is the most abundant and affordable type of opal. It usually origin from South Australian fields though some from other areas.
Crystal opal is transparent and is pure opal (hydrated silica.) It typically has sharp clarity of diffracted color visible from within and on the surfaces of the opal. When held out of the direct light, crystal opal displays some of the most intense opal color. And White opal is the most common type of precious opal and is translucent with a creamy appearance which dominates the diffracted colors. All of the opal fields produce white opal with most of it being mined in Coober Pedy.
Black or darkish bodied opal with bright specs of colour. This is chemically treated Limestone matrix with precious opal in voids. Not common. Andamooka South Australia opal field is the main mining area of Andamooka Matrix Opal.
Precious opal with a grey or darkish appearance when viewed from the front. Dark opal is relatively abundant.
Usually Lightning Ridge area in NSW or Mintabie in South Australia
Rarer than light or dark opal.
Black opal is principally found at Lightning Ridge in New South Wales, Australia. This magnificent gemstone is the most valuable form of opal. It's dark background color, usually black, blue, brown or gray, sets the spectral colors ablaze much like a storm cloud behind a rainbow. Black Opal is a gemstone that has had an important effect overseas, as a product of Australia. It requires a precise meaning so that the quality of this gem can be meaningfully established.
Whether an opal is a black or not can be determined by nearly closing ones eyes and squinting at the face of the stone. All colours are ignored and the overall body tone (blackness level) can then be seen. When this is compared to the scale of blackness given in Figure 1 below it is possible to identify how black the stone is.
Only stones achieving values N1 to N4 on this scale are considered black opals - attracting the additional value associated of this class of opal.
In addition to solid opal, a number of other varieties composite opal are widely available. Composite stones are generally more affordable than solid stones as beautiful slices, instead of opal stone as a whole, are cut from previous opal stone and being used. In all cases, thin slices of opal are glued to a backing of black backing material to enhance the bright colour of opal slice.
While most composite stones are made from natural opal, occasionally synthetic opal is used in doublets or triplets.
Doublets are made by gluing slices of precious opal to a common opal (potch) backing with blackened cement, usually an epoxy resin. The dark backing enhances the colors of the opal. When the backing is brown ironstone it is often called a boulder doublet.
Thin slice of precious crystal opal glued between crystal cap on top and black backing.
Thin chips of precious crystal opal glued onto black backing, can be used in doublets, triplets or on watch faces.