Beryl, Al₂Be3Si₆O₁₈

Beryl, Al₂Be3Si₆O₁₈, is another beautifully crystalline aluminium mineral. It is hexagonal (hohohedral; a:c = 1:0.4989); hardness, 7.5; density, 2.7. The pale green crystals known as aquamarine, and the dark green crystals known as emerald, are familiar as precious stones. Beryl has been synthesised by Hautefeuille and Perrey.