Abstract
1. Chrysoberyl, BeAl 2 O 4 , is analogous in chemical composition to spinel, MgAl 2 O 4 , and the other members of the spinel group, but it bears no resemblance to them in its crystalline form. The spinels are cubic, and have a very simple structure, which has been analysed by S. Nishikawa and W. H. Bragg, The same type of structure has been discovered in other compounds, Chrysoberyl belongs to the orthorhombic holohedral class, the axial ratios being a : b : c = 0·4707 : 1 : 0·5823. The “ a ” axis is an axis of pseudo-hexagonal symmetry. The angle (011) : (011) is 60° 26', and the ratio of b to c is very nearly √3 : 1 or 1 : 0·577. The crystal twins in a manner very similar to that of aragonite, three individuals interpenetrating so as to form what appears to be a simple hexagonal crystal. The examination of the structure is interesting for two reasons. Firstly, it is curious that it shows such contrast to that of a spinel. Secondly, the axial ratios are almost identical with those of the olivine group of minerals, and are nearly given by the ratio √ ⅔ : 1 : √3/3.
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Schedule a callMore From: Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character
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