Emerald is the green variety of the gemstone beryl, and is a particularly beautiful stone when set in fine jewellery. The name emerald is derived from the Greek smaragdos via the Old French esmeralde, and means simply green gemstone. In ancient Rome, green was the colour of Venus, the goddess of beauty and love.

The earliest known source of emerald was near the Red Sea in Egypt, in Cleopatra's famous emerald mines. They were probably worked from about 2000 B.C. Apparently their location was lost in the middle ages and not rediscovered until 1818. Most emeralds used in ancient jewellery are believed to have come from these mines.

The most famous current source of emeralds in the world is at Muzo and Chivor in Colombia, where they are found, very unusually, in limestone. The Incas and Aztecs also made use of South American emeralds and regarded them as holy. Emeralds are also found in South Africa, Brazil, and the Urals. In the United States emeralds are mostly found in North Carolina.

Most emeralds are oiled – immersed in oil (usually green) which fills up the many cracks and fissures which are frequently found in emerald. As this makes the inclusions less visible, oiled emeralds usually have improved clarity and an enhanced colour due to the green of the oil.

The emerald with the highest cost-per-carat ever sold was auctioned off in 2000 by Christies, who sold the 10 carat stone for over $1 million, equivalent to over $100,000 per carat. The mention of emeralds in the Vedas as auspicious and having healing properties made them especially popular with Indian nobility, and breathtaking emeralds have been found amongst the possessions of maharajas and maharanis. The largest of these is the so-called Mogul Emerald, inscribed with prayer texts and ornate floral designs. This is dated from 1695, weighs 217.8 carats and is 10cm tall. This was sold by Christies to an unidentified buyer for $2.2m, in 2001.

Marlene Dietrich was apparently a particular fan of fine jewellery containing emeralds and often wore her own in her films. One anecdote tells of her baking a cake at Katherine Cornell’s house, and being unable to find her 37.41-carat cabochon emerald ring which she had taken off in the kitchen. Despite everybody’s best efforts, the ring could not be found – until it turned up in a piece of the cake during dessert!