precious opal

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.

Most gem-stones are harder than quartz, though precious opal, turquoise, moonstone and sphene are inferior to it in hardness.

This distinction is reserved almost wholly for the variety known as noble or precious Opal.

Precious opal, translucent with beautiful play of colors, used as a gem.