Australian Grey Opal Red-Green-Blue Navette Cabochon

About Grey Opal

Grey opal is a descriptive colour category rather than a separate mineral species. Its body colour ranges from pale smoke-grey to charcoal, blue-grey or brownish grey. Some specimens are common opal and show no play-of-colour; others are precious opal and display shifting flashes of green, blue, yellow or red when moved in the light. Opal is hydrated, amorphous silica: it has no orderly crystal structure and contains variable…