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Opal is a hydrated amorphous form of silica (SiO 2 · n H 2 O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline forms of silica, which are considered minerals. It is deposited at a relatively low temperature and may occur ...
An excellent example of watermelon tourmaline jewelry is a brooch piece (1969, gold, watermelon tourmaline, diamonds) by Andrew Grima (British, b. Italy, 1921–2007), in the collection of Kimberly Klosterman and on display at the Cincinnati Art Museum. [19] Some forms of tourmaline are dichroic; they change color when viewed from different ...
A collection of tourmaline cabochons in a variety of colours. A cabochon (/ ˈkæbuʃɒn /; from Middle French caboche 'head') is a gemstone that has been shaped and polished, as opposed to faceted. The resulting form is usually a convex (rounded) obverse with a flat reverse. [1] Cabochon was the default method of preparing gemstones before ...
Gemstone. Group of precious and semiprecious stones—both uncut and faceted—including (clockwise from top left) diamond, uncut synthetic sapphire, ruby, uncut emerald, and amethyst crystal cluster. A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or ...
Opals. 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.
In 1912, to standardize birthstones, the (American) National Association of Jewelers (now called Jewelers of America) met in Kansas and officially adopted a list. [1]: 317 The Jewelry Industry Council of America updated the list in 1952 [3]: 311 by adding Alexandrite for June, citrine for November and pink tourmaline for October.
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