Twisted crystals: Propagation, genesis, and relationships with optical activity and molecular symmetry (excerpts)

With respect to the screw-like twisting of many crystals, Wallerant has already supposed that twisting is related to a structure dissymetrique of the crystals. In accordance with Pasteur's law, such bodies will in general crystallize in enantiomorphic forms and possess at least the possibility of optical activity. In a few cases, Wallerant has observed a direct relationship between the sense of optical rotation of the substance and the twisting direction of the crystals. The research has dealt only with substances that the literature identifies as possessing holohedric symmetry, lacking optical rotatory power, but nonetheless exhibiting twisted forms. At the same time, it was found that the presence of foreign impurities did not just influence the twisting but was its sole cause in many cases. An obvious further step was to relate the screw-shaped deformation of crystals with the far more frequently observed simple curvature; finally, an attempt was made to elucidate the mechanism of curvature or twisting.