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Communication from the Oxford Mineralogical Laboratory

Published online by Cambridge University Press:  14 March 2018

H. L. Bowman
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Extract

The stones to which this paper refers were sent to Prof. Miers for determination by Mr. Francis Powell, and were stated to come " from the diamond washings." They are of a fine green colour, and quite transparent, and possess a highly perfect cleavage parallel to the faces of a prism having an angle of about 88°. This serves to distinguish the material from olivine, which it otherwise much resembles, and --coupled with the uniformly straight extinction through cleavage flakes, the specific gravity (3.199) and hardness (6-7)--suffices to identify the mineral as one of the rhombic pyroxenes.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 12 , Issue 58 , November 1900 , pp. 349 - 362
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1900

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References

page 350 note 1 The perfect prismatic cleavage rendered this a process of some difficulty. I found fine carborundum, used with water on an iron or pewter lap, to be the most convenient grinding material, as flour emery is exceedingly slow in action, and a coarser emery is very apt to break the specimen along the cleavages.

page 351 note 1 The difference between the values of β as calculated from the axial angle and as measured with the prism, may perhaps be due to a variation in the optical characters of the three specimens used, corresponding to a slight observed differ. ence in the specific gravity. The prism value is probably the most reliable.

page 354 note 1 By exposing cD'stals of Gypsum from Bex to a temperature of about 100° in an air bath, Pape (Pogg. Ann. cxxxv. 4, 1868) obtained elliptical figures pointing to the existence of an ellipsoid (" Verwitterungsellipsoid ") similar to those calculated by him in the case of copper sulphate, &c. Later observers, e.g. Sohneke (l.c.), have produced by the same method polygonal and not elliptical spots.

page 356 note 1 Axial angle, a=85°47', (a: c=1: 1.363).

page 359 note 1 a:b:c=0.9693:1:0.9256 B=76°20' (E. S. Dana.)

page 359 note 2 Angles obtained by method of maximum illumination