Prized since ancient times, a fine emerald can be more expensive than a high quality diamond of the same carat weight. Emerald is a form of Beryl, which occurs in many other colors depending on the impurities that Mother Nature has mixed into its otherwise clear formula. Blue beryl is known as aquamarine. Pink shades of beryl are known as Morganite. Yellows are often just called yellow beryl and golden beryl. The term bixbite refers to red beryl, a variation that's even more rare than emeralds. Learn what you need to know about emeralds before you shop for emerald jewelry.