Opal is a unique and highly valued gemstone known for its stunning play-of-color and variety of forms. Unlike most gemstones, it is hydrated silica rather than a crystalline mineral.
Opals are prized for their play-of-color, a phenomenon where rainbow-like flashes of color appear as the stone moves.
Hardness
5.5 – 6.5 on the Mohs scale
Softer than quartz or beryl, so requires careful handling in jewelry
Color
Opal comes in a wide variety of types and colors:
Base Colors
White / milky
Black / dark
Blue, green, orange, pink, red
Special Effects
Play-of-color: Flashing rainbow colors caused by diffraction of light in silica spheres
Fire opal: Transparent to translucent orange or red, may or may not show play-of-color
Boulder opal: Opal veins in ironstone, often with vibrant flashes
Where It’s Found
Australia – the main source (Coober Pedy, Lightning Ridge, Andamooka)
