Opal is an amorphous hydrated silicon oxide, chemical formula It is precipitated from silica-bearing waters in voids and fissures of certai

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Opal is an amorphous hydrated silicon oxide, chemical formula It is precipitated from silica-bearing waters in voids and fissures of certain rocks. Water molecules trapped in the silica framework account for the milky lustre and brilliant pastel colours that make opal such a desirable precious stone. Specimen is from Opal Butte, Oregon, USA and actual width is 75 mm.

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Photo credit: © DIRK WIERSMA/SCIENCE PHOTO LIBRARY / Alamy / Afripics
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Keywords: amorphous, butte, crust, fissures, gemstone, glassy, globules, hostrock, hydrated, hydrous, iridescent, jewellery, jewelry, luster, lustre, mineral, mineralogy, opal, orange, oregon, precipitation, silica, siliceous, void