Olympic Australis is a noted one (4)
I believe the answer is:
opal
(Other definitions for opal that I've seen before include "Milky-white mineral" , "Rock" , "Many-coloured gem" , "Gem stone" , "Gem with delicate colours" .)
I believe the answer is:
opal
(Other definitions for opal that I've seen before include "Milky-white mineral" , "Rock" , "Many-coloured gem" , "Gem stone" , "Gem with delicate colours" .)