Birthstone: May

Hardness: 7.5-8

Emerald has been prized for thousands of years for its lush green hues and rare beauty. Throughout the ancient world, emerald symbolized eternal hope, rebirth and the arrival of spring - and some cultures believed the gem rewarded its owners with love, intelligence and eloquence as well.

In ancient Rome emeralds were believed to have a soothing effect on the soul. Modern scientists have since shown this myth to have some basis in fact: tests indicate that the human eye is more sensitive to green than any other color. Middle Age seers used emeralds to foretell the future, as well as to ward off evil spirits and cure ailments ranging from bad eyesight to infertility. The stone was also said to improve memory and bring great wealth to its wearer.

The finest emeralds have traditionally come from Colombia; both the Incas and Aztecs mined rich emerald deposits in the rugged Andes Mountains. But Russia's Ural Mountains also have produced top-quality gems. Brazil is by far the world's largest producer of emerald, with a wide range of quality. Other sources for the stone include Afghanistan, Australia, India, Pakistan, the United States, Zambia and Zimbabwe.

Emeralds come in a variety of light and dark shades of green - and often with subtle background hues of other colors like yellow, blue, brown or gray. Generally, the purer and richer the green, the more valuable the emerald. While its relatively hard, emerald can still be scratched, chipped or split fairly easily. Most emeralds have numerous flaws, or "inclusions", which weaken their structure. Flawless emeralds are exceptionally rare, and therefore command great prices (in some instances, higher than diamonds).

Like most gemstones in the market today, emeralds are usually treated in some way to remove surface flaws and enhance color. The most common (and acceptable) technique is to oil the stone with a green-tinted oil to fill in surface cracks. The oil hardens and strengthens the stone, and improves its green color as well. In caring for your emerald, avoid ultrasonic cleaners that can remove the oil, or harsh cleansers that can damage its relatively soft surface. Clean with a soft, damp cloth and warm water, and a soft bristle brush if needed.