Aquamarine is a form of beryl, a mineral made up of beryllium, aluminum, silicon, and oxygen. Its color ranges from pale to light to yellowish blue; other gem-quality beryls include emerald (blue green to green), goshenite (colorless), morganite (pink to violet), and heliodor (golden). The blue color is caused by traces of iron in the beryl, and it may fade with prolonged exposure to light.
Like other forms of beryl, aquamarine crystals form a hexagonal prism. They can often become quite large, in sharp contrast to its emerald cousins. The largest aquamarine ever found was 19 inches long, 16 inches wide, and weighed 243 pounds before it was cut. In addition, it rarely has any visible flaws; an 879.5 carat flawless aquamarine resides in the British Museum of Natural History. It has a mineral hardness of 7.2 to 8.
Aquamarine's name comes from the Latin words for "sea water", for its color. In the Roman Empire, aquamarine was considered to have medicinal and healing powers for the jaws, stomach, and liver and to have the power to see the future. It is said that Nero possessed an eyeglass made of aquamarine.
In the Middle Ages it was additionally believed to be an antidote against poison and the treasure of mermaids, lending it the power to keep sailors safe at sea. It was supposed to help married couples work out differences, provide courage, quicken the wit, and protect against the devil's manipulations.
Naturally-occurring deep blue aquamarines are the rarest and most valuable. Green-hued gems are least valuable, but the blue color of any aquamarine are commonly enhanced through heating. Aquamarine is sometimes called the "poor man's diamond" because it is so common and affordable. It is mined in Brazil, Columbia, Madagascar, Russia, Sri Lanka, Colorado, and North Carolina.
Aquamarine is not synthesized because it is so common -- the cost of doing so exceeds the cost of mining it naturally -- but synthetic blue spinel is sometimes used in its place. Light blue topaz is very similar to aquamarine in both color and physical properties and is sometimes substituted as well.
Aquamarine is the traditional birthstone for the month of March and is the symbolic gemstone for the 19th wedding anniversary.