Synthetic emeralds grown hydrothermally in an alkali-free, chlorine-bearing solution have been manufactured in Guilin, China, since 1987.

Some gem diamonds fluoresce, most commonly blue, to the concentrated long-wave ultraviolet radiation of a UV lamp.

Commercial quantities of gem-quality benitoite are known from a single location in the world, the Benitoite Gem mine in the New Idria district of San Benito County, California.

New mining techniques have combined state-of-the-art equipment and technology to detect and extract large, fine-quality rhodochrosite specimens and gem rough.

Examination of 51 colorless to near-colorless synthetic diamonds from all known sources of production confirms that they can be distinguished from similar-appearing natural diamonds on the basis of their gemological properties.

Ruby crystals from Southeast Asia with a fixed six-rayed star, similar in effect to trapiche emeralds from Colombia, are described.

The Capão mine is one of the oldest and most productive fully mechanized Imperial topaz mines in the historic Ouro Preto area of Minas Gerais, Brazil.

Among the most difficult gems to identify are those that are black and opaque (or nearly so).

Two instruments have been developed at De Beers DTC Research Centre, Maidenhead, to distinguish synthetic diamonds from natural diamonds.

Since 1993, large amounts of gem-quality sapphires from the Andranondambo region of southern Madagascar have entered the international gem market.

Opal occurs as nodules in volcanic rocks at a new gem opal locality in the Menz Gishe district of Shewa Province, Ethiopia.

Demantoid, green andradite garnet, was discovered in the Central Ural Mountains of Russia in the mid-19th century.

A new type of Russian hydrothermal synthetic emerald is produced by seeded growth in steel autoclaves without noble-metal inserts; the seed slices have been cut parallel to a face of the second-order hexagonal dipyramid s (1121).

This article explores the mining developments and new diamond occurrences in Africa that led to many of the key concepts in modern geology.

For more than 100 years, Africa has produced large commercial quantities of diamonds and important individual stones.

One of the most interesting of the commercially available Czochralski pulled synthetic corundums is pink “Ti-sapphire.”

The emeralds of the Ural Mountains, in what is now called the Russian Federation, have been known for more than 160 years.