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Hydrous micas

Published online by Cambridge University Press:  14 March 2018

George Brown  and
Keith Norrish
George Brown
Affiliation:
Pedology Department, Rothamsted Experimental Station, Harpenden
Keith Norrish
Affiliation:
Pedology Department, Rothamsted Experimental Station, Harpenden
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Extract

Hydrous micas differ from normal micas in that they contain less potassium and more water. In the calculation of structural formulae from their chemical analyses, two methods have been used which rely on the following different assumptions:

1. As these minerals are often fine-grained and may contain adsorbed water, no reliance is placed on the value of H2O+ (water lost above 105° C.) as a measure of structural water. The water content is ignored and the structural formula is calculated on the basis of 20 oxygens plus 4 hydroxyls per structural unit. This method has been used by Hendricks and Ross and by Grim and Bradley.

2. The water which is recorded as H2O+ in the chemical analysis is assumed to represent hydroxyl groups in the aluminosilicate layers of the minerals. Thus, instead of having 20 oxygens and 4 hydroxyl ions per structural unit as in normal micas, formulae are derived which show less than 20 oxygens and more than 4 hydroxyls, the total oxygen plus hydroxyl remaining 24. This method has been used by Brammall, Leech, and Bannister.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 29 , Issue 218 , September 1952 , pp. 929 - 932
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1952

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References

page 929 note 2 We take as the structural unit a cell of volume abc sin β/m, where a, b, c, and fl are the unit–cell parameters, and m is the number of layers per unit cell. This structural unit is chosen as it is independent of polymorphism of micas (S. B. Hendricks and M. E. Jefferson, Amer. Min., 1939, vol. 24, p. 729 [M.A. 7–496]).

page 929 note 3 Hendricks, S. B. and Ross, C. S., Amer. Min., 1941, vol. 26, p. 683. [M.A. 8–275.]Google Scholar

page 929 note 4 Grim, R. E. and Bradley, W. F., Chapter V in X–ray identification and crystal structures of clay minerals. Min. Soc., London, 1951. [M.A. 11–253.]Google Scholar

page 929 note 5 Brammall, A., Leech, J. G. C., and Bannister, F. A., Min. Mag., 1937, vol. 24, p. 507 CrossRefGoogle Scholar.

page 929 note 6 Shishkin, N. V., Zhurn. Obshchei Khim. (Acad. Sci. U.S.S.R.), 1951, vol. 21, p. 456 Google Scholar.

page 930 note 1 Grim, R. E., Bray, R. H., and Bradley, W. F., Amer. Min., 1937, vol. 22, p. 813.Google Scholar [M.A. 7–12.]

page 930 note 2 Gruner, J. W., Amer. Min., 1934, vol. 19, p. 557 Google Scholar. [M.A. 6–181.]

page 932 note 1 Ganguly, A. K., Soil Sci., 1951, vol. 71, p. 239 CrossRefGoogle Scholar. [M.A. 11–450.]