Opalite is an opal-dominated rock (opal = amorphous hydrous silica = SiO2·nH2O).  “Opal” is a mineral/mineraloid name.  “Opalite” is a rock name.  Opalites form principally by alteration of volcanic rock or alteration of siliceous sinter (a type of hot spring deposit).  They are often described as “impure” opal rocks.  They lack the famous “fire” & rainbow colors of gem-grade opal.


The opalite shown below comes from the B and B Mine in Nevada's mercury belt, western Esmeralda County, southwestern Nevada, USA.  The disseminated reddish material is cinnabar (HgS - mercury sulfide).


Opalite (field of view ~3.2 cm across) with cinnabar (= disseminated reddish) from a paleo-hot spring deposit in Nevada, USA.




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