Beryl

Beryl
Three varieties o beryl: morganite, aquamarine an heliodor
General
Category	Cyclosilicate
Formula (repeatin unit)	Be3Al2(SiO3)6
Strunz clessification	09.CJ.05
Creestal seestem	Hexagonal
Space group	Hexagonal dihexagonal dipyramidal H-M symbol (6/m 2/m 2/m) Space group: P 6/mmc
Unit cell	a = 9.21 Å, c = 9.19 Å; Z = 2
Identification
Formula mass	537.50
Colour	Green, blae, yellae, colourless, pink an ithers
Creestal habit	Prismatic tae tabular cystals; radial, columnar; granular tae compact massive
Twinnin	Rare
Cleavage	Imperfect on {0001}
Fractur	Conchoidal tae irregular
Tenacity	Brickle
Mohs scale haurdness	7.5–8
Skinkle	Vitreous tae resinous
Streak	White
Diaphaneity	Skyre tae leamin
Speceefic gravity	Average 2.76
Optical properties	Uniaxial (-)
Refractive index	nω = 1.564–1.595 nε = 1.568–1.602
Birefringence	δ = 0.0040–0.0070
Pleochroism	Waik tae distinct
Ultraviolet fluorescence	Nane (some fractur fillin materials uised tae improve emerald's clarity dae fluoresce, but the stane itsel daes nae)
References

In geology, beryl is a meeneral componed o beryllium aluminium cyclosilicate wi the chemical formula Be₃Al₂(SiO₃)₆. The hexagonal crystals o beryl mey be vera smaa or range tae several meters in size. Terminated crystals is relatively rare. Pure beryl is colourless, but it is frequently tintit bi impurities; possible colours are green, blae, yellae, reid, an white.