Opal

colourless, white, grey, yellow, brown, blue, red, violet, orange, black

Transparent, Translucent, Opaque

blue, blue-white, white, green, green-yellow, rarely yellow or red

green, yellow

inclusions: swirl-like resolutions, goethite, chalcedony etc, liquid- and multiphase inclusions, porous: d sometimes difficult to measure; often doublets/triplets

for red, orange: see= fire Opal

5 - 6

SiO₂ + H₂O

Amorphous

1