Opal is a form of silica; its water content is usually between 6 and 10% Because of its amorphous character. Opal is the national gemstone of Australia. Australian opal has often been cited as accounting for 95-97% of the world’s supply of precious opal, with the state of South Australia accounting for 80% of the world’s supply.
The internal structure of precious opal makes it diffract light; depending on the conditions in which it formed, it can take on many colors.
Precious opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the black opals are the most rare, whereas white and greens are the most common. It varies in optical density from opaque to semitransparent.
