Crystallography and Mineralogy (kesshogaku kobutsugaku), 11th volume in the series Introduction to Modern Earth Science published by the Japanese company Kykoritsu, is a small textbook composed of 11 chapters, three appendices, two appendix tables and one plate, that clearly targets students and young researchers in Earth and Planetary Sciences with a practical approach to the investigation of mineral samples. Given the small size of the book, the topics are necessarily presented in a rather concise way and selected from what could have been a wider choice. The text is well written with a pedagogical approach: a beginner reading this book will have a rather clear idea of the general features of the samples and of what information (s)he may get from the main experimental techniques: for a more in-depth approach one will however need to move to more specialistic textbooks. The first two chapters, which span only seven pages, summarize the type of samples that are the focus of the treatment and the techniques used for their chemical and structural investigation. Geometric crystallography is the object of chapter 3 (‘geometry and symmetry of a crystal’, 18 pages), which is the weakest in this book. It makes constant reference to the 1972 edition of International Tables for X-ray Crystallography; for a text appearing in 2015, the choice of such an outdated reference is hard to understand and certainly not justified. A number of imprecisions affect this chapter which, because of the very limited space, reduces to little more than a list of definitions. Note in Table 3.1 we read about a ‘trigonal lattice’ (sampo koshi), which simply does not exist, trigonal being a word reserved for a crystal system: the ‘other’ lattice in the hexagonal family is rhombohedral (hishigata koshi). On the same page, we read that the symmetry of the lattice leads to a classification in a crystal system (shkokei), which is untrue, the result being lattice systems (koshikei). The same mistakes are repeated on page 18, whereas the figure on p. 19 correctly shows a rhombohedral cell: the contradiction should be selfevident. On p. 12 the definition of geometric element is incorrectly applied to the symmetry element. In the next page a curious listing of eight ‘independent symmetry elements’ is given, which does not make much sense. Firstly, if the list really concerns symmetry elements, as suggested by the fact that 3 and 6 are missing (being considered the combination of 3 and 1 and of 3 and m perpendicular to it, respectively), then the identity should not appear because it obviously has no ‘element’. Secondly, if the list includes symmetry operations instead, as suggested by the presence of the identity, then one could list only 6 and 1, the repeated application of either or both of them generating all the ten types of operations in crystallography point groups. Whatever interpretation is adopted, the statement remains incorrect. Fig. 3.5 in the following two pages gives the stereographic projection of the 32 types of crystallographic point groups where, however, the cubic centrosymmetric groups are given as m3 and m3m instead of m3 and m3m (same problem in Table 1 of the appendix): an unjustifiable remnant of prehistoric times when typographical issues primed over consistency (3 includes 3 as even powers, whereas the opposite is not true). Table 3.3 in the next page gives [100] instead of [110] as the tertiary symmetry direction of tetragonal crystals; furthermore, only one direction (square brackets) is given instead of a representative set of equivalent directions (angular brackets) for cubic and uniaxial crystals, and the direction chosen does not follow international standards: this certainly comes from the questionable decision of choosing as a reference an old mineralogy book by Morimoto et al. (1975) instead of International Tables. No time to breathe, another imprecision follows immediately: the orthographic ISSN 2052-5206
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Oct 14, 2024
Dario Croccolo + 2
Open Access
