Halos contain information about the interfacial angles within a crystal, the refractive index and hence the chemical composition of the solid, the crystal symmetry
, the shape of the crystals, and the orientation that falling crystals assume in the air.
As mentioned above, enlarging the PBGs by the reduction of crystal symmetry
by anisotropic anisotropy is not a good choice, since the asymmetry of diamond lattice provides a better way to open the band gaps at high-symmetry points in the Brillouin zone.
For the second monoclinic modification, it is further noted that the metric symmetry (Table 4) exceeds the crystal symmetry--i.e., the metric symmetry is F-centered orthorhombic whereas the crystal symmetry
is reported as C-centered monoclinic (Space Group Cc).
The benitoite crystal symmetry
(ditrigonal dipyramidal) had been postulated to exist but was not known in nature until the discovery of the species.
The first two chapters present an overview of crystal symmetry
and the line properties of dislocations.
Table 1 Lattice parameters calculated from electron diffraction of Flabellina iodinea crystals, simulated biogenic polymorphs, and anhydrous guanine Source Crystals purified Crystals purified from cerata, from body, experimental ([Angstrom]) experimental ([Angstrom]) Lattice dimension a 6.60 [+ or -] 0.03 6.54 [+ or -] 0.02 Lattice dimension b 13.64 [+ or -]0.02 13.66 [+ or -]0.05 Lattice dimension c 18.77 [+ or -]0.04 18.76 [+ or -]0.02 Crystal symmetry
Undetermined (c) Undetermined (c) Source [lambda].-polymorph, Guanine anhydrous, (b) simulated (a) ([Angstrom]) experimental ([Angstrom]) Lattice dimension a 6.38 3.55 Lattice dimension b 9.73 9.69 Lattice dimension c 18.39 16.35 Crystal symmetry
Orthorhombic Monoclinic Source [beta]-polymorph.
However, in ice [I.sub.sd] the crystal symmetry
dictates that two sets of alternating faces are symmetry independent (Fig.
In order to satisfy this condition, the two sets of two-level transitions should be selected according to the selection rules under a certain crystal since the crystal symmetry
plays a role in determining the transition probabilities .