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Beryl [Be3Al2Si6O18]
Structure Hexagonal
Space Group : P6/mcc
(No. 192)
a=9.2080 Å c=9.1880 Å
a=b=90.00, g=120.00
Z=2
Atomic Positional Parameters
Be 6f 0.5000 0.0000 0.2500
Al 4c 0.3333 0.6667 0.2500
Si 12 0.3876 0.1159 0.0000
O1 12l 0.3103 0.2369 0.0000
O2 24m 0.4985 0.1456 0.1453
Reference
RM Hazen, AY Au and LW Finger (1986)
American Mineralogist, 71, 977-984
Mineral Chemistry
The Si6O18
ring is the basic framework of the structures of beryl and tourmaline.
In beryl, Si6O18
rings are arranged in layers parallel to {0001}, with sheets of beryllium (Be) and aluminium (Al) ions lying between the layers of rings. Beryllium coordinated by four oxygens, and aluminium coordinated by six oxygens tie the rings together. Within the channels formed by Si6O18
rings, OH-, H2O,
F-, Rb+, Cs+,
Na+ or K+ may be found. The chemical formula given above does not incorporate these substituted ions or molecules.
Beryl occurs in granite pegmatites, in mica schists, marbles, and nepheline-syenites. Emerald is a deep green beryl, aquamarine pale greenish-blue, and morganite pale pink. Beryl may be synthesized from SiO2, Al2O3 and BeCO3 at high pressure and temperature under hydrothermal conditions.
The CHIME figure shows aluminums as grey, beryls as crimson, silicons as ochre, and oxygens as red spheres. Sodiums in the channels formed by the silicate rings are shown as large blue spheres.