·noun A rare metallic element, of a silver white color, and low specific gravity (2.1), resembling magnesium. It never occurs naturally in the free state, but is always combined, usually with silica or alumina, or both; as in the minerals phenacite, chrysoberyl, beryl or emerald, euclase, and danalite. It was named from its oxide glucina, which was known long before the element was isolated. Symbol Gl. Atomic weight 9.1. Called also beryllium.