opal

n. iridescent semi-precious stone of hydrated silica

For other OPAL articles, see Opal (disambiguation).''OPAL (Open Pool Australian Lightwater reactor) is a 20 megawatt pool-type nuclear research reactor that was officially opened in April 2007 at the Australian Nuclear Science and Technology Organisation (ANSTO) Research Establishment at Lucas Heights in south Sydney, Australia. The Argentine company INVAP S.E. was the main contractor responsible for the delivery of the reactor, performing the design, construction and commissioning. Reactor commissioning is currently ongoing.
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The mineraloid opal is amorphous SiO2·''nH2O, hydrated silicon dioxide, the water content sometimes being as high as 20 ut is usually between three and ten percent. Opal ranges from clear through white, gray, red, yellow, green, shore, blue, magenta, brown, and black. Of these hues, red and black are the most rare and dear, whereas white and green are the most common; these are a function of growth size into the red and infrared wavelengths—see precious opal. Common opal is truly amorphous, but precious opal does have a structural element. The word opal comes from the Latin opalus, by Greek òpalliòs, and is from the same root as Sanskrit upálá[s] for "stone", originally a millstone with upárá[s] for slab. (see Upal). Opals are also Australia's national gemstone.
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Noun
1. a translucent mineral consisting of hydrated silica of variable color; some varieties are used as gemstones
(hypernym) mineral
(hyponym) black opal
(derivation) opalize, opalise

n. opal, iridescent semi-precious stone

n. opal, girasole