The phenomena of the play of colours in precious opal has not been satisfactorily explained.
precious opal was found by Klaproth to consist of silica, 90; water, 10; which is a very curious combination.
precious opal, translucent with beautiful play of colors, used as a gem.
The bird had deposited in the mother's lap an egg which beamed like the precious opal with many-coloured brilliancy.
"precious opal" is distinguished from "common opal" by the beauty of its display rather than by any difference in composition.
This distinction is reserved almost wholly for the variety known as noble or precious opal.
Thus the precious opal now much admired was hardly known in former times.