A mineral of great hardness, and, when transparent, of much beauty. It occurs in hexagonal prisms, commonly of a green or bluish green color, but also yellow, pink, and white. It is a silicate of aluminium and glucinum (beryllium). The aquamarine is a transparent, sea-green variety used as a gem. The emerald is another variety highly prized in jewelry, and distinguished by its deep color, which is probably due to the presence of a little oxide of chromium.
- 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.