A precise set of remarkable geological and geochemical conditions is required for the formation of these brilliant green gems. Beryllium, essential for the crystallisation of beryl, is one of the most elusive elements in the Earth’s crust (estimated to be about 2 parts per million) and must be carried up to the surface by pegmatites, which, in turn, must come into contact with chromium and vanadium-bearing (ultramafic) rocks in order to attain the desired colour. Not all pegmatites are beryllium-bearing and even fewer are emplaced within rocks that contain adequate chromium. These factors – coupled with even more specific temperature, pressure and fluid content requirements for its formation – makes emerald extremely rare and remarkably erratic in its distribution.