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Aquamarines

Beryl
Beryl09.jpg
Three varieties of beryl: morganite, aquamarine and heliodor
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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