From teaching experience. IV. Three questions from the course of crystal morphology

The article is devoted to three questions from the course of crystal morphology, which are not considered in detail in the popular university textbook of crystallography by G. M. Popov and I. I. Shafranovsky (any edition): on the table of 32 species of symmetry (ambiguous position of some species of symmetry and meaning of inversion axes), on the number of simple forms possible on crystals (47 or 48), on the symbols of simple forms in trigonal and hexagonal syngonies (the sum of the first three indices always equals zero). The history of crystallography is rich in instructive subjects. Their use in lectures seems to be a useful methodological technique.