One of the most popular exhibits at the Smithsonian Institution, the stunning Fancy Dark grayish blue Hope diamond was formally graded by GIA’s gem laboratory.

This article reports on the study of six diamonds, both before and after a filling treatment, and the examination of 12 additional filled stones.

A plastic imitation opal that shows true play-of-color was advertised as

The world-renowned Sinkankas collection of books and other publications is now available to the public as part of the Richard T. Liddicoat Gemological Library and Information Center at GIA Santa Monica.

Recent mining at Opal Butte in northeastern Oregon has produced a wide variety of large flawless opals.

Brazil is currently the leader in overall production of amethyst.

With the increasing use of radiation to color enhance gemstones, the issue of radioactivity has become a source of concern for gemologists worldwide.

A pair of sharp absorption bands in the near-infrared region, referred to as H1b and H1c, have been detected in one (and the H1b band in the other) of two green diamonds known to have been treated.

A gem-quality iridescent orthoamphibole from Wyoming, similar to that described from Greenland, has been identified.

The diamond industry was buffeted by extreme price volatility during the last decade, unlike any encountered since the Great Depression of the 1930s.

Pyrope garnets occur in near-colorless to light orange and pink, as well as the familiar red.

The final part of this series is concerned with colors explained by band theory, such as canary yellow diamonds, or by physical optics, such as play-of-color in opal.

The techniques for cutting and polishing gemstone giants.

Mining fine cat's-eye chrysoberyl and alexandrite in Brazil.

This is the second part in a three-part series on the origin of color in gem materials.

The authors determined that there are actually seven types of

This article reviews the history of the conch "pearl," discusses S. gigas and its fisheries, and examines the gemological properties and other characteristics of this attractive material.

Examination of a group of 14 brownish yellow, yellow, and greenish yellow synthetic diamonds reveals distinctive gemological properties.

This three-part series of articles reviews our current understanding of gemstone coloration.

An examination of the two types of sugilite found at the Wessels mine in South Africa.