On the Crystallographic Orientation of Spatial Branches in Natural Polycrystalline Snow Crystals

Abstract

As a part of the study on polycrystalline snow crystals, the angles between spatial branches of natural snow crystals were measured at the summit of Mt. Teine, utilizing a universal stage.
It was found that the predominant angle was variable according to the crystal types of polycrystalline snow crystals, however the highest peak in the distribution of the angle was recognized around 70° in the all types of polycrystalline snow crystals. It was also found that a-axes of spatial branches are common to those of the basal plane in the snow crystal with spatial branches, as far as detected.
Based on the fact described above, the lattice misfit of ice crystal was analyzed, consequently it was confirmed that the value of 70° angle of the spatial branches to the basal plane corresponds to the angle between (3032) and (0001) planes, and that the amount of the lattice misfit between the two planes is nearly zero.
The result of this analysis appears to show that the matching theory is very useful to explain the angle of spatial branches to the basal plane etically, however, some questions were presented to the theoretical explanation.