beryl (bĕrˈĭl) [key], mineral, a silicate of beryllium and aluminum, Be3Al2Si6O18, extremely hard, occurring in hexagonal crystals that may be of enormous size and are usually white, yellow, green, blue, or colorless. Beryl is commonly used as a gemstone. The refractive index is low, and the stones have little or no fire. The most valued variety of beryl is emerald. An aquamarine is a blue to sea-green beryl; morganites are rose-red beryls. It is the principal raw material for the element beryllium and its compounds.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
More on beryl from Fact Monster:
See more Encyclopedia articles on: Mineralogy and Crystallography