Emerald is a precious variety of the mineral beryl. It forms in granite and pegmatiterocks, taking its colour from additional chromium and vanadium atoms. Emerald crystals are long prisms, clearly hexagonal in shape with faceted, domed terminations. Inclusions can identify origin: for example, stones containing calcite or pyrite come from Brazil; those with mica, from Russia or Africa.High quality, transparent stones are rare and go to the gem trade, but opaque emerald with cloudy inclusions are easy to find.