Welcome, May, and your birthstone: the Emerald!
There are only four precious gemstones—and emeralds are one of them, making them highly valuable. And because emeralds are so susceptible to flaws, a perfect emerald is extremely rare. For this reason, emeralds traditionally are graded with the naked eye (not high magnification) which creates a little extra tolerance for the beautiful green gem. Like other gemstones, color is paramount; great emeralds have a deep, bright color. But clarity is also very important—more so than with most other stones.
Emeralds are a variety of Beryl and its green color is due to chromium "impurities" within the stone. They were mined in Egypt as early as 1500 BC. They've also been found in the New World—and Cortez is known to have wowed the Spanish court with his impressive booty of the stones. Today, half the world's emeralds come from Columbia. Another 20% come from Zambia.
The American Art Deco cufflinks, above, are not made of emerald. They do, however, have a beautiful emerald green enameling. Please click on the photo above to learn more about them.