Chemical Formula: Be3Al2Si6O18
Color: Any color, but is usually light green, yellow, or blue
Importance: Has two main uses. First, it is used as a gemstone. Both emeralds and aquamarine are forms of beryl. The second use is as a source of beryllium, which is a very light and strong metal. Beryllium from beryl is used in high strength machine parts and spacecrafts due to its lightness and toughness.
Other Interesting Information: Ideally, beryl is colorless. But due to impurities from other elements, its color changes. For example, emeralds are green due to Cr3+, and aquamarine is blue due to Fe2+.
My Take: Like most minerals, many people know varieties of beryl but do not know the mineral itself. This is unfortunate because beryl itself is one of the most beautiful minerals in existence.
For More Information: http://www.minerals.net/mineral/beryl.aspx