Editing Opal (section)

==Common opal==
[[File:Common Rough Opal.jpg|thumb|alt= A rock set on a black background with a scale in millimetres at the bottom edge. It shows a mixture of light brown rock with translucent white rock on the underside.|Common rough opal]]
[[File:SLOVAKIAN OPAL 12.jpg|thumb|alt=Four opals on a black background. Their opalescence is relatively low, appearing more as translucent blue and white rock than opal proper.|White and blue opal from Slovakia]]

Besides the [[gemstone]] varieties that show a play of color, the other kinds of common opal include 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;<ref>{{cite book|last=Gribble|first=C.&nbsp;D.|title=Rutley's Elements of Mineralogy|publisher=Unwin Hyman|location=London|year=1988|edition=27th|page=431|chapter=Tektosilicates (framework silicates)|isbn=978-0-04-549011-0}}</ref> [[menilite]], which is brown or grey; [[hyalite]], a colorless glass-clear opal sometimes called Muller's glass; [[geyserite]], also called [[siliceous sinter]], deposited around [[hot springs]] or [[geyser]]s; and [[diatomaceous earth]], the accumulations of [[diatom]] shells or tests. Common opal often displays a hazy-milky-[[turbidity|turbid]] sheen from within the stone. In [[gemology]], this optical effect is strictly defined as opalescence which is a form of adularescence.