In geology, beryl is a mineral composed of beryllium aluminium cyclosilicate with the chemical formula Be₃Al₂(SiO₃)₆. The hexagonal crystals of beryl may be very small or range to several meters in size. Terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, red, and white.