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On the chemical classification of the mica group. I. The acid micas

Published online by Cambridge University Press:  14 March 2018

A. F. Hallimond
A. F. Hallimond*
Affiliation:
Museum of Practical Geology, London, 1
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Extract

In a discussion of the composition of glauconite, it was shown that the analyses of this substance can be represented in terms of simple molecular proportions, provided that the mineral is regarded as a mixture of a silicate containing the group R2O3 with a similar compound in which one equivalent of R2O8 is replaced with one equivalent of RO; the general formula being R2O. 4(R2O3, RO). 10SiO2. nH2O.

Work on the sedimentary iron ores collected during the preparation of the ‘Special Reports on Mineral Resources’, recently issued by the Geological Survey, made it necessary to review the composition of some of the chlorites ; but no evidence of similar replacement was found among the better-known minerals of that group.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 20 , Issue 109 , June 1925 , pp. 305 - 318
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1925

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References

Page 305 note 2 Hallimond, A. F. and Radley, E. G., Min. Mag., 1922, vol. 19, pp. 330–333.CrossRefGoogle Scholar

Page 306 note 1 Calcium, which is present in unimportant amounts, is omitted except in the analyses by Kunitz, where it is included in the RO group.

Page 306 note 2 Boeke, H. E., Neues Jahrb. Min., 1916, vol. 1, pp. 83–117 Google Scholar. [Min. Abstr., vol. 1, p. 245.]

Page 306 note 3 Kunitz, W., Neues Jahrb. Min., 1924, Beihlge-Band 50, pp. 365–413 Google Scholar. [Min. Abstr., vol. 2, p. 424.] This valuable paper was read at the annual meeting of the German Mineralogical Society in 1922, and a preliminary abstract was published in Zeits. Krist., 1923, vol. 57, pp. 559-561. The details of the 32 new analyses were published while the present paper was in manuscript. The analyses, recalculated to SiO2 = 600, have been included in the present tables, and they fully confirm the earlier data. In many important respects the formulae assigned by Kunitz are in agreement with those here given. As regards the RO oxides, however, that author denies on ‘valency-thcoretical’ grounds that RO can replace R2O3 (p. 389) ; the phengites are explained as resulting from accidental inclusions (p. 378); and even the ferric oxide in lepidomelane is attributed to secondary alteration by reversible reaction between FeO and water (p. 389). Nevertheless it is recognized that lepidolite can be derived from muscovite by substituting Lifo for Al2O3 ; but phlogopite is derived from muscovite by putting 6RO in place of 2Al2O3 (p. 396) ; and the author concludes that without synthetic experiments a complete explanation of the valency difference between Li and A1 cannot be obtained. An attempt is made to deal with the question by means of complex groups such as [2 Li, Si], called ‘Le’, thus the lithia micas are written KH2Al2Le[SiO4]3 ; a formula which does not accord with the constant ratio K2O:6SiO2. The use of basic alumina radicles does not seem to have been considered, although early in the paper a reference is made to topaz. (See note on p. 318.)

Page 310 note 1 Bowman, H. L., Min. Mag., 1902, vol. 13, p. 98 CrossRefGoogle Scholar; Baumhauer, H., Zeits. Kryst. Min,, 1912, vol. 51, pp. 344–357 Google Scholar.

Page 311 note 1 Clarke, F. W., Bull. U.S. Geol. Survey, 1914, no. 588, p. 55.Google Scholar

Page 315 note 1 W. and D. Asch, The silicates in chemistry and commerce. London, 1913.