#192
P6/mcc
Example – Beryl, Al2Be3(SiO3)6(H2O)0.0991
From the ancient Greek, beryllos, signifying a “precious blue-green color of sea water” stone, but through later usage, applied only to Beryl.
Structure and thermal expansion of Beryl
Morosin, B.
Acta Crystallographica B (1972) 28, p1899-p1903
SiO4 tetrahedra (orange)
BeO4 distorted tetrahedra (blue)
AlO6 distorted octahedra (blue-grey)
The Fascination of Crystals and Symmetry 