Popular varieties are Emerald, Aquamarine and Morganite. Beryl is also available in pale lemon yellow to intense golden yellow known as Heliodor and also in paler green tones. It is a bright durable gem with a hardness of 7.5 – 8 with an attractive vitreous lustre. The yellow colours are a good lower cost alternative to yellow Sapphire as they are more common in larger sizes than Sapphire. Beryl is doubly refractive with an RI of 1.563 – 1.582 and specific gravity 2.68 – 2.80.