Aquamarine Description An aquamarine crystal in its natural state shows why these specimens are prized for their beauty. - Courtesy of Daniel Trinchillo, Fine Minerals International Aquamarine is the green-blue to blue variety of the mineral beryl. (Emerald is the green to bluish green variety of the same mineral.) Its colour is usually a light pastel greenish blue. This 20.83-carat stone from Africa represents the large size and attractive colour that make aquamarine a much-prized gem. - De'ev Dvir/ICA, courtesy Gemstar Ltd., IsraelHeat treatment usually gives it a more bluish appearance. Aquamarine crystals are known to be large in size and relatively clean and well-formed, making them particularly valuable to collectors of mineral specimens.