Hues range from single color, two or three colors, or all the colors of the rainbow. Silica in the opal causes display of background color. The most common opal is an opaque white stone.
Ancient Romans called opal the Queen of Gems. More recently, in 2008, NASA’s explorations of Mars revealed the presence of opal on that planet.
Use in jewelry:
Because it's soft and brittle, opal jewelry should be treated gently. To make the most of the internal play of color, cabochon cuts are popular.
5.5-6.5 (1 softest to 10 hardest).
Permeation with colorless wax, oil, plastic and hardeners to improve appearance and durability. All treatments must be disclosed.
Wipe with a soft cloth.