Opals evolved from the Greek Opallios
Opal ranges from clear through white, grey, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black.
The effect seen in Opals is due to water and some can hold up to 20%
The Greeks beleived that the stone made the wearer see the futre,The stones were common with theives as they beleived that the stone made you invisible.
Australia produces 97% of all opals
Synthetic Opals contain substances not found in natural opal (e.g., plastic stabilizers). The imitation opals seen in vintage jewellery are often "Slocum Stone" consisting of laminated glass with bits of foil interspersed.