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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 ...

For the first time ever, the famous Hope diamond was graded by a widely recognized system. Although the 45.52-ct weight was confirmed, the GIA Gem Trade Laboratory graders found the clarity—recently ...

Figure 1. Sapphires from a variety of sources. Faceted stones (left to right): 6.36 ct pink/orange (padparadscha), 1.63 ct pink, 4.76 ct violet, 5.43 ct violet purple, 3.03 ct blue, 2.12 ct blue, 8.06 ...

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 ...

Diamond “type” is a concept that is frequently mentioned in the gemological literature, but its relevance to the practicing gemologist is rarely discussed. Diamonds are broadly divided into two types ...

Figure 1. These emeralds from Musakashi, Zambia, range from 0.57 to 4.85 ct. The rough samples were polished with one window on each. The faceted sample measures 6.29 × 5.35 × 3.53 mm and weighs 0.97 ...

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 ...

A new diamond imitation, synthetic moissanite (silicon carbide), is now being produced by C3 Inc. in near-colorless form for jewelry purposes. With refractive indices of 2.648 and 2.691, a dispersion ...

Lapis lazuli is an aggregate of several minerals. Lazurite grains provide its characteristic blue color, while golden flakes of pyrite can add attractive contrast. Lapis lazuli is a rock, which means ...

Natural pearls grow in the wild without human intervention. They are very rare, and most natural pearls in the market today are antique. Cultured pearls are grown in pearl farms, and are the direct ...

This 7.19-carat alexandrite was cut to feature its beautiful color change. When the light source changes from daylight to incandescent light, the gem’s color changes from bluish green to reddish ...