Aquamarine crystal. Aquamarine is a transparent blue or bluegreen variety of beryl (beryllium aluminium silicate). The colour is due to trace amounts of iron within the crystal structure. Beryl occurs in many colours; green beryl is termed emerald. The rare, transparent beryl varieties are used as gemstones, while the more common types form the principal ore of the metal beryllium, which is widely used in industrial alloys. The main producer of aquamarines is Brazil. They are also found in Pakistan and the USA.