Opal, Three Mile Hill mine, Coolgardie, WA Collection Highlights | Updated 1 week ago Precious opal from the Three Mile Hill mine near Coolgardie, Western Australia. Peter Downes, WA Museum Light is dispersed into a beautiful play of colours by orderly arrays of tiny silica spheres in this thin vein of precious opal (SiO2·nH2O). Donated to WA Museum Boola Bardip by The Foundation for the WA Museum in recognition of the contribution made by Jenny Allen. See this specimen on display in the Origins gallery. Gem Collection