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  2. Spinel - Wikipedia

    en.wikipedia.org/wiki/Spinel

    It is widely used as an inexpensive cut gem in birthstone jewelry for the month of August. Light blue synthetic spinel is a good imitation of aquamarine beryl, and green synthetic spinel is used as an emerald or tourmaline simulant. [29] By 2015, transparent spinel was being made in sheets and other shapes through sintering. [30]

  3. Chrysoberyl - Wikipedia

    en.wikipedia.org/wiki/Chrysoberyl

    Chrysoberyl is the third-hardest frequently encountered natural gemstone and lies at 8.5 on the Mohs scale of mineral hardness, between corundum (9) and topaz (8). [ 7 ] An interesting feature of its crystals are the cyclic twins called trillings .

  4. Taaffeite - Wikipedia

    en.wikipedia.org/wiki/Taaffeite

    Taaffeite (/ ˈ t ɑː f aɪ t /; BeMgAl 4 O 8) is a mineral, named after its discoverer Richard Taaffe (1898–1967) who found the first sample, a cut and polished gem, in October 1945 in a jeweler's shop in Dublin, Ireland. [4] [5] As such, it is the only gemstone to have

  5. Diamond simulant - Wikipedia

    en.wikipedia.org/wiki/Diamond_simulant

    Gem-quality material is usually a strong yellow to honey brown, orange, red, or green; its very high RI (2.37) and dispersion (0.156) make for an extremely lustrous and fiery gem, and it is also isotropic. But here again, its low hardness (2.5–4) and perfect dodecahedral cleavage preclude sphalerite's wide use in jewelry.

  6. Black Prince's Ruby - Wikipedia

    en.wikipedia.org/wiki/Black_Prince's_Ruby

    The gemstone at the front of the Imperial State Crown. The Black Prince's Ruby is a large, irregular cabochon red spinel weighing 170 carats (34 g) set in the cross pattée above the Cullinan II diamond at the front of the Imperial State Crown of the United Kingdom.

  7. Gemology - Wikipedia

    en.wikipedia.org/wiki/Gemology

    Gem identification is basically a process of elimination. Gemstones of similar color undergo non-destructive optical testing until there is only one possible identity. Any single test is nearly always only indicative. For example: The specific gravity of ruby is 4.00, glass is 3.15–4.20, and cubic zirconia is 5.6–5.9 . So one can easily ...

  8. Hercynite - Wikipedia

    en.wikipedia.org/wiki/Hercynite

    Hercynite is a spinel mineral with the formula FeAl 2 O 4. It occurs in high-grade metamorphosed iron-rich argillaceous (clay-containing) sediments as well as in mafic and ultramafic igneous rocks. Due to its hardness it also is found in placers. [2]

  9. Chelsea filter - Wikipedia

    en.wikipedia.org/wiki/Chelsea_filter

    The "chelsea" filter was originally devised by Anderson and Payne in 1934 of the Gem testing Laboratory of the London Chamber of Commerce & Industry.The filter was devised with the collaboration of gemmology students of the Chelsea College of Science and Technology where Basil Anderson was an instructor for the Gemmological Association of Great Britain.

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