Emerald

Overview

Emerald is the green variety of beryl, coloured by traces of chromium, vanadium or both. Few gems are judged so strongly by colour: a richly coloured emerald with visible inclusions is worth far more than a pale, clean one. Those inclusions, which gemmologists call the jardin ("garden"), are part of the stone's character and help prove that it is natural.

Colour

The finest emeralds are a pure to slightly bluish green of medium to medium-dark tone, with strong, even saturation. Stones that are too light are usually sold as green beryl rather than emerald. Colour also differs by source: classic Colombian stones tend towards a warm, glowing green, while Zambian emeralds, which owe part of their colour to iron, are often a cooler, slightly bluish green.

Key properties

Where emeralds come from

Colombia's Muzo, Chivor and Coscuez mines have set the standard for centuries. Zambia (especially the Kafubu area) is now one of the largest producers, and Zimbabwe's Sandawana deposit is known for small, intensely coloured stones. Brazil, Afghanistan's Panjshir valley, Ethiopia, Madagascar and Russia's Ural mountains also produce fine material.

Treatments

Almost every emerald on the market has been clarity enhanced: fissures that reach the surface are filled with a colourless oil or resin so they show less. The treatment is accepted by the trade but must be disclosed, because fillers can dry out, discolour or leak over time. A laboratory report describes the amount of enhancement; untreated emeralds of good colour are rare and command a premium. Dyed emeralds and coloured fillers are not acceptable without explicit disclosure.

Durability

Emerald is hard enough for jewellery, but its inclusions make it more brittle than its hardness suggests. Protective settings (bezels, or claws that guard the corners) suit rings worn every day, and the classic emerald cut, with its cut corners, was developed partly to reduce the risk of chipping.

Buying tips

• Colour first. Choose the most vivid, evenly distributed green your budget allows.
• Accept inclusions, but not weaknesses. Look for inclusions that do not reach the surface near corners or the girdle.
• Ask about enhancement. Request the degree of filling in writing, ideally on a report from a recognised laboratory.
• Origin can add value, but only a laboratory can determine it.

Care and cleaning

Clean emeralds with warm water, a mild soap and a soft brush, then dry them with a lint-free cloth. Avoid ultrasonic and steam cleaners, solvents and sudden temperature changes, all of which can disturb fillers. Remove emerald rings for gardening, sport or heavy work, and have the setting checked once a year.