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Aquamarine is a variety of Beryl that is transparent and of various shades of blue and blue-green; almost all of the specimens of the preferable sky-blue colour are (since 1920) the result of heat treatment applied to greenish or yellow-brown beryls. The stones are dichroic, and are usually cut as a brilliant or step cut. They resemble the Emerald (the chemical composition is identical, as is the hexagonal crystal form) but the stones are paler and, being less rare, are much less valuable. They also resemble euclase and blue Topaz, from all of which (as well as from glass imitations and synthetic gemstones) they can readily be distinguished.
There are many sources, but Brazil has produced the finest and some very large specimens, e.g. one found in 1919 weighing 110.2 kg. (243 Lb). Some ancient aquamarines were engraved with portraits, e.g. one with a portrait of Julia, daughter of the Roman Emperor Titus. The synthetic stone resembling aquamarine is the blue Synthetic Spinel.