Aquamarine
The sea-blue variety of beryl — emerald's clearer, hardier cousin, coloured by iron.
Also known as: Blue beryl
beginner Granitic pegmatites
What it is
Aquamarine is the blue to blue-green variety of beryl (beryllium aluminium silicate), coloured by iron. It shares beryl's hardness of 7.5 to 8 on the Mohs scale but, unlike emerald, typically grows as clean, transparent crystals with few inclusions, so large eye-clean stones are readily available.
The most valued colour is a pure, saturated blue; much rough is naturally greenish and is routinely heat-treated to remove the yellow component and deepen the blue, a stable and accepted treatment. Brazil is a historic source, along with Pakistan, Nigeria, Madagascar and Mozambique. Aquamarine is the traditional birthstone for March.