Common opal

Besides the gemstone varieties that show a play of color, there are other kinds of common opal such as the milk opal, milky bluish to greenish (which can sometimes be of gemstone quality), resin opal which is honey-yellow with a resinous luster, wood opal which is caused by the replacement of the organic material in wood with opal[6], menilite which is brown or grey, hyalite is a colorless glass-clear opal sometimes called Muller's Glass, geyserite, also called siliceous sinter, deposited around hot springs or geysers and diatomite or diatomaceous earth, the accumulations of diatom shells or tests.