**Vladislav V. Gurzhiy**

Department of Crystallography, Institute of Earth Sciences, St. Petersburg State University, University Emb. 7/9, St. Petersburg 199034, Russia; vladislav.gurzhiy@spbu.ru or vladgeo17@mail.ru

Received: 4 September 2020; Accepted: 9 September 2020; Published: 11 September 2020

**Keywords:** mineral; crystallography; crystal chemistry; X-ray diffraction; crystal structure; crystal growth; mineral evolution

Crystallography remains, for mineralogy, one of the main sources of information on natural crystalline substances. A description of mineral species shape is carried out according to the principles of geometric crystallography; the crystal structure of minerals is determined using X-ray crystallography techniques, and physical crystallography approaches allow one to evaluate various properties of minerals, etc. However, the reverse comparison should not be forgotten as well: the crystallography science, in its current form, was born in the course of mineralogical research, long before preparative chemistry received such extensive development. It is worth noting that, even today, investigations of the crystallographic characteristics of minerals regularly open up new horizons in materials science, because the possibilities of nature (fascinating chemical diversity; great variation of thermodynamic parameters; and, of course, almost endless processing time) are still not available for reproduction in any of the world's laboratories. This Special Issue is devoted to mineralogical crystallography, the oldest branch of crystallographic science, and combines important surveys covering such topics as: discovery of new mineral species; crystal chemistry of minerals and their synthetic analogs; behavior of minerals at non-ambient conditions; biomineralogy; and crystal growth techniques.

We hope that the current set of reviews and articles will arouse genuine interest among readers and, perhaps, push them to their own successful research in the field of mineralogical crystallography.
