Opal Facts

Colour: Opal can be a light milky colour with flashes of iridescence. 
Black opal has variations of blues and greens with flashes of iridescence.
Fire Opal has a beautiful translucent orange colour.
Hardness: 6 (on Moh’s hardness scale).
Specific Gravity: 2.10. This is an indication of the stone's density, calculated by comparing the stone's weight with the weight of an equal volume of water.
Refractive Index: 1.37 to 1.47. This is a measure of the amount light is bent from its original path when passing through a stone.
Chemical composition: Hydrated silica gel.
Principal sources: Australia, USA, Brazil, Mexico and Southern Africa.