Aquamarines
| Beryl | |
|---|---|
Three varieties of beryl: morganite, aquamarine and heliodor
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| General | |
| Category | Cyclosilicate |
|
Formula (repeating unit) |
Be3Al2(SiO3)6 |
| 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 |
| Luster | Vitreous to resinous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| 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 |
| 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 | |
Beryl is a mineral composed of beryllium aluminium cyclosilicate with the chemical formula Be3Al2(SiO3)6. 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, red, and white.
The name "beryl" is derived (via Latin: beryllus, Old French: beryl, and Middle English: beril) from Greek βήρυλλος beryllos which referred to a "precious blue-green color-of-sea-water stone"; akin to Prakrit verulia, veluriya ("beryl"). The term was later adopted for the mineral beryl more exclusively.
When the first eyeglasses were constructed in 13th century Italy, the lenses were made of beryl (or of rock crystal) as glass could not be made clear enough. Consequently glasses were named Brillen in German (bril in Dutch and Briller in Danish).
Beryl of various colors is found most commonly in granitic pegmatites, but also occurs in mica schists in the Ural Mountains, and limestone in Colombia. Beryl is often associated with tin and tungsten ore bodies. Beryl is found in Europe in Norway, Austria, Germany, Sweden (especially morganite), Ireland and Russia, as well as Brazil, Colombia, Madagascar, Mozambique, Pakistan, South Africa, the United States, and Zambia. US beryl locations are in California, Colorado, Connecticut, Georgia, Idaho, Maine, New Hampshire, North Carolina, South Dakota and Utah.
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