Beryl

Beryl is a mineral composed of beryllium aluminium silicate with the chemical formula Be₃Al₂Si₆O₁₈. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring hexagonal crystals of beryl can... Wikipedia

• Category:  Cyclosilicate
• Strunz classification:  9.CJ.05
• Crystal system:  Hexagonal
• Crystal class:  Dihexagonal dipyramidal (6/mmm), H-M symbol: (6/m 2/m 2/m)
• Space group:  P6/mcc
• Unit cell:  a
• Formula mass:  537.50 g/mol
• Color:  Green, blue, yellow, colorless, pink, and others
• Crystal habit:  Prismatic to tabular crystals, radial, columnar, granular to compact massive
• Twinning:  Rare
• Cleavage:  Imperfect on
• Fracture:  Conchoidal to irregular
• Tenacity:  Brittle
• Mohs scale hardness:  7.5–8.0
• Luster:  Vitreous to resinous
• Streak:  White
• Diaphaneity:  Transparent to translucent
• Specific gravity:  2.63–2.92
• Optical properties:  Uniaxial (−)
• Refractive index:  n ω
• Birefringence:  δ
• Pleochroism:  Weak to distinct
• Ultraviolet fluorescence:  None (some fracture-filling materials used to improve emerald's clarity do fluoresce, but the stone itself does not). Morganite has weak violet fluorescence.
• Data source:  DuckDuckGo