Aquamarine (Be3Al2SiO6) composed of Beryllium aluminum silicate is the greenish-blue to blue variety of Beryl. It forms in beautiful crystals that can be quite large and totally transparent. Unlike Emerald which usually is flawed or heavily included. Aquamarine can form in stunning flawless crystals. It's hardness on the Mohs scale is 7.5-8.
There are many localities but the most known ones are Brazil, Pakistan, Nigeria, Madagascar, Namibia, China, USA.