Emerald; The Birthstone for May The mineral world celebrates the month of May with a special green gemstone; Emerald. Emerald is the greenish variety of a family of minerals known as beryl which also includes aquamarine (which is the blue variety), heliodor (golden-yellow variety), morganite (orange-pink variety). Beryl, which is beryllium aluminum silicate, is a rare mineral with a chemical composition of Be3Al2(SiO3)6. In its pure form, beryl is white