Beryllium is an essential constituent of about 100 out of about 4000 known
minerals, the most important of which are
bertrandite (Be4Si2O7(OH)2),
beryl (Al2Be3Si6O18),
chrysoberyl (Al2BeO4), and
phenakite (Be2SiO4). Precious forms of beryl are
aquamarine and
emerald.