Emerald
| Emerald | |
|---|---|
| General | |
| Category | Beryl variety |
| Formula | Be3Al2(SiO3)6 |
| Crystal system | Hexagonal (6/m 2/m 2/m) Space group: P6/mсc |
| Space group | (6/m 2/m 2/m) – dihexagonal dipyramidal |
| Unit cell | a = 9.21 Å, c = 9.19 Å; Z = 2 |
| Identification | |
| Formula mass | 537.50 |
| Color | Bluish green to green |
| Crystal habit | Massive to well Crystalline |
| Cleavage | Imperfect on the [0001] |
| Fracture | Conchoidal |
| Mohs scale hardness | 7.5–8 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to opaque |
| Specific 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 |
| Ultraviolet fluorescence | None (some fracture-filling materials used to improve emerald's clarity do fluoresce, but the stone itself does not) |
| References | |
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Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium. Beryl has a hardness of 7.5–8 on the Mohs scale. Most emeralds have many inclusions, so their toughness (resistance to breakage) is classified as generally poor. Emerald is a cyclosilicate.