Aquamarine

Aquamarine is a variety of Beryl, the same gemstone as Emerald. Technically Aquas are just light blue emeralds but instead of them containing higher amounts of chromium impurities which would cause a green color, it contains more iron impurities which gives it the notorious sky blue color

Hardness: 7.5 – 8
Composition: Be₃Ai₂Si₆O₁₈