Aquamarine is the greenish-blue to blue variety of Beryl. Aquamarine can form in stunning flawless crystals, creating some of the most beautiful mineral masterpieces. Crystals are prismatic, often with flat terminations, hexagonal, and without striations. Beryl is a mineral that contains a significant amount of beryllium. Beryllium is a very rare metal, and that limits the formation of beryl to a few geological situations where beryllium is present in sufficient amounts to form minerals.