Beryl
Beryl (/ˈbɛrəl/ BERR-əl) 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 be up to several meters in size, but terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, pink, and red (the rarest). It is an ore source of beryllium.
| Beryl | |
|---|---|
| General | |
| Category | Cyclosilicate |
| Formula (repeating unit) | Be3Al2Si6O18 |
| IMA symbol | Brl |
| 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 = 9.21 Å, c = 9.19 Å; Z = 2 |
| Identification | |
| 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 {0001} |
| 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 | nω = 1.564–1.595 nε = 1.568–1.602 |
| Birefringence | δ = 0.0040–0.0070 |
| 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. |
| References | : 112 |
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