Emerald
The green variety of beryl — valued for its vivid colour despite near-universal inclusions.
Also known as: Green beryl
intermediate Hydrothermal veins and pegmatites
What it is
Emerald is the green gem variety of beryl (beryllium aluminium silicate) coloured by chromium and sometimes vanadium. It is 7.5 to 8 on the Mohs scale, hard enough for jewellery but brittle: emeralds almost always contain fissures and inclusions, poetically called the jardin ("garden"), which make them more fragile than ruby or sapphire.
Because of that fragility, the vast majority of emeralds are treated with oils or resins to fill surface-reaching fractures and improve apparent clarity — a long-accepted practice that must be disclosed. Colombia produces the most celebrated stones, with Zambia and Brazil also major sources. The finest emeralds show a pure, saturated green with strong colour even in smaller sizes.