A transparent to translucent glassy mineral, essentially aluminum beryllium silicate, Be3Al2Si6O18, occurring in hexagonal prisms and constituting the chief source of beryllium. Transparent varieties in white, green, blue, yellow, or pink are valued as gems.
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.