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This large Australian light opal cabochon weighs 117.85 carats. Small play-of-color flashes of orange and green predominate in a pinfire pattern, with spots of a more muted blue over a grayish ...

This is the second chart in G&G’ s series focused on micro-features often observed in natural, treated, and synthetic gems. Sapphire (figure 1) was chosen because of its enduring importance within the ...

This amethyst crystal is from Namibia. It shows classic quartz crystal shape: a six-sided columnar crystal with a pyramid-shaped termination at the top. Courtesy Daniel Trinchillo, Fine Minerals ...

This 17.53-carat amethyst displays a rich reddish purple color. - Lydia Dyer, Super Trillion Cut Amethyst gem courtesy of John Dyer & Co. Amethyst has been the most-prized quartz variety for centuries ...

Figure 1. The five zircon samples used in this study, ranging in size from 0.56–21.92 ct, were analyzed for radioactive degradation of their crystal structure. Radioactive elements such as thorium and ...

Zircon’s typical greenish blue color has been referred to as zircon blue. - Lydia Dyer, gem courtesy of John Dyer & Co. Zircon is a gemstone that’s not commonly known among jewelry buyers, which is a ...

Sapphire comes in a variety of colors. This rare 1,126.00-ct. corundum crystal’s pinkish orange color is called padparadscha, named after the lotus flower. - © GIA ...

A 43-carat alexandrite in the collection of the British Museum. Abundant alexandrite deposits were first discovered in 1830 in Russia’s Ural Mountains. Those first alexandrites were of very fine ...

A listing of prominent auction houses specializing in gemstones and fine jewelry. The following list has been compiled for informational purposes only and does not imply endorsement by GIA. This is a ...

Figure 1. Sapphires from Madagascar: a beautiful 3.29 ct untreated faceted stone and an assortment of rough in the background. Madagascar has produced many high-quality stones in the last few years ...

This chart focuses primarily on the types of natural inclusions found in tourmaline, as well as the minerals in which tourmaline can be found as an inclusion. Treatments such as enhancement of ...