Abstract
IN this elementary text-book the information is given mainly in the form of a series of definitions, and is not easy to follow, even with some previous knowledge of the subject. A beginner, especially one attempting to work alone, would very likely soon become hopelessly confused. The book is, however, no doubt intended for the author's own students in the University of Arizona. The various hemihedral and tetartohedral “divisions” of each system are developed by the older method of suppression of certain faces or groups of faces of the holohedral form, and little use is made of the more important ideas of symmetry. The number of the planes of symmetry appertaining to each division is, however, clearly stated; but reference to axes of symmetry is omitted, except in the incorrect definition: “A symmetry axis is a line or direction perpendicular to a symmetry plane and passing through the centre of the object.” Another definition runs: “A hemimorphic crystal is one in which the law of axes is violated”; and such crystals are disposed of in some other division. Including hemimorphic crystals, twenty-two of the thirty-two possible crystal-classes are dealt with, but, since for some of them there are no examples amongst minerals, the statement on the title-page is rather beside the point. Precise instructions for “orienting crystals” are repeated under each crystal-class, but, strange to say, few of the text-figures are set quite straight on the page. By an unfortunate error the title of the book appears on the cover as “Geometrical Chrystallography.”
A Manual of Geometrical Crystallography. Treating solely of those Portions of the Subject useful in the Identification of Minerals.
Prof.
G. Montague
Butler
By. Pp. viii + 155. (New York: John Wiley and Sons, Inc.; London: Chapman and Hall, Ltd., 1918.) Price 7s. net.
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A Manual of Geometrical Crystallography Treating solely of those Portions of the Subject useful in the Identification of Minerals . Nature 103, 103 (1919). https://doi.org/10.1038/103103b0
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DOI: https://doi.org/10.1038/103103b0