This structure lends itself to cameo making. Contra luz opals are transparent opals that show a brilliant play of iridescence only when light shines through the stone. Opals have a hardness of 5.5 to 6.5 and a specific gravity of 1.98-2.50. Opals are found in many placees worldwide, but Australia has a tremendous variety of beautiful opals. An opal doublet is a manufactured stone that is composed of two thin layers that are glued together.
Opal glass is a milky white glass that mimics opals.
An opal triplet is a manufactured stone that is composed of three thin layers that are glued together. A thin layer of opal is sandwiched between a layer of clear quartz and a layer of either obsidian or ironstone. An opal triplet is an opal doublet with a quartz layer on top. Triplets must be cleaned very carefully. Open-ended necklaces usually have ornaments, like beads or tassels, at the ends.