Opal Characteristics:
Precious opal is a gemstone that exhibits flashes of rainbow-like colors when viewed from different angles. The colors are created by an arrangement of silica spheres within the opal. Common opal does not have this flash of color.
Opal Colors:
Opals have a light or dark body color that may be either translucent or transparent. The opals we see most often in jewelry have a milky-white base with varying flashes of color.
Black opals are the most rare and expensive opals, with a body color that can range from dark grey to black with fiery flashes of color. Precious fire opals are another alternative. They have base colors ranging from yellow to orange, and can be transparent to translucent with fiery flashes.
Opal Hardness:
Opal hardness varies, but generally ranges from 5.5 to 6.5 on the Mohs scale. Compare that to diamond, which rated at 10 is the hardest gem.
Opal Care:
Do not use harsh cleansers on your opals and do not clean opals with ultrasonic cleaners. Never rub oil on an opal, because although it makes the fire brighter it can damage the opal. Some jewelers recommend you periodically soak opals in water to help them reabsorb lost moisture.
Opal Mining:
Australia is the leading source for opals. but a great number of fire opals are found in Mexico. Other sources of precious opals include Africa, the United States, Brazil, areas of the former Soviet Union and Nicaragua.
Opal Doublets and Triplets:
Opal doublets and triplets are composite stones that are made by positioning a thin layer of opal on top of a chunk of glass or less expensive gemstone. To find a composite, inspect the sides of an opal, looking for indications that it's really a stack of layers. You can also check the stone's base to see if it matches the top. If it doesn't it might be a composite.
