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Each of the three notable types of opal – precious, common, and fire [3] – display different optical effects; therefore, the intended meaning varies depending on context. The general definition of opalescence is a milky iridescence displayed by an opal, which describes the visual effect of precious opal very well, and opalescence is ...
Gem-quality opal, or precious opal, has a wonderful rainbow play of colors (opalescence). This play of color is the result of light being diffracted by planes of voids between large areas of regularly packed, same-sized opal colloids. Different opalescent colors are produced by colloids of differing sizes.
Precious opal consists of spheres of silica molecules arranged in regular, closely packed planes (idealized diagram). This precious rough opal from Coober Pedy, South Australia, displays nearly every color of the visible spectrum. Precious opal shows a variable interplay of internal colors, and though it is a mineraloid, it has an internal ...
Andamooka Opal, presented to Queen Elizabeth II, also known as the Queen's Opal; Flame Queen Opal; Galaxy Opal; Halley's Comet Opal, the world's largest uncut black opal; Olympic Australis Opal, reported to be the largest and most valuable gem opal ever found
Sometimes, fossils are preserved in opal or precious opal. The gorgeous black opal shown above is from a relatively newly discovered deposit in northern Ethiopia. A widespread nodule horizon of black precious opal occurs at the boundary between a lithified volcanic ash unit and a clay bed. The opal nodules are hosted in clay.
Labradorite (Spectrolite) – Ylämaa, Finland. Labradorite ((Ca, Na)(Al, Si) 4 O 8) is a calcium-enriched feldspar mineral first identified in Labrador, Canada, which can display an iridescent effect ().
The Yowah opal field in the Shire of Paroo. The Yowah nut is a type of precious opal, found within the Yowah opal fields situated in Yowah, Shire of Paroo, South West Queensland, Australia since the latter part of the 19th century. [1] These opals are known for their distinctive nut-like shape, opalescent patterns, and vibrant colours.
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