Abstract
THE opinion is rapidly gaining ground that the theory of crystallography based on the laws of rational indices and symmetry no longer suffices without modification for the classification and description of crystals. It is recognised on the one hand that isomorphism of kindred substances shows itself (as in the Humite group of minerals) more in similarity of crystalline habit and angles than in identity of optical and geometrical symmetry, and on the other hand that vicinal faces with high indices may play an important part in the economy of crystals. Prof. Viola is evidently of opinion that the old methods cannot be adapted to meet the situation, and his book is as revolutionary as it well could be. Crystals are here divided into 7 sygonies, 10 fundamental forms, and 29 harmonies; symmetry is but a particular case of harmony; twins are two similar crystals with two predominant elements in common; the number of space-lattices is reduced to 10, and of space-groups to 156. The basis of classification is descriptive, not geometrical; blende, felspar, and garnet belong to the same fundamental form, chalcopyrite and tetrahedrite to the same harmony.
Grundzüge der Kristallographie.
By Prof. C. M. Viola. Pp. iv + 389. (Leipzig: W. Engelmann, 1904.) Price 11 marks; bound, 12 marks.
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HILTON, H. Grundzüge der Kristallographie . Nature 71, 340 (1905). https://doi.org/10.1038/071340a0
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DOI: https://doi.org/10.1038/071340a0