GIA’s Gem Encyclopedia is a virtual journey through the science and lore of gemstones from across the globe. Each precious stone page features additional detailed gemological information, a buyer’s …

Some of the world’s most valuable colored stone deposits formed in only two geological events. The first such event involved the collision of east and west Gondwana from around 650-500 million years ago, …

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Tourmalines have a variety of exciting colors with one of the widest color ranges of any gem species, occurring in various shades of virtually every hue.

The first installment of this column discusses the formation of colored stones from the crust-mantle transition and below.

Identifies the type of colored gemstone, natural or synthetic, informed opinion on geographical origin based on research and known samples, describes detectable treatments, details a full description of …

Amethyst Gemstone is the purple variety of the Quartz mineral. Amethyst’s purple color can range from a light lilac to a deep, intense royal purple, and from brownish to vivid.

Both of these gemstones are known for their endless color combinations and are believed to have been created from rainbows. Learn more about these two birthstones for October and discover their …

This course provides basic, essential knowledge of colored stones, with an in-depth focus on the “Big Three” of the gemstone world: ruby, sapphire, and emerald.

Gem diamonds in GIA’s D-to-Z range usually decrease in value as the color becomes more obvious. Just the opposite happens with fancy color diamonds: Their value generally increases with the …