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Gedrite from Glen Urquhart, Inverness-shire

Published online by Cambridge University Press:  14 March 2018

G. H. Francis
G. H. Francis*
Affiliation:
Department of Mineralogy, British Museum
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Abstract

This note describes a hydrous gedrite from Glen Urquhart for which the presence of an appreciable excess of oxygen atoms over the normal 96 per unit cell has been established. This is associated with an approximately equal deficiency of cations. The type of isomorphous replacement here discussed is hitherto unrecorded in the amphibole group.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 30 , Issue 230 , September 1955 , pp. 709 - 716
Copyright
Copyright © 1955, The Mineralogical Society

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References

page 709 note 1 Heddle, M.F., Min. Scotland, 1901, vol. 2, p. 40.Google Scholar

page 710 note 1 Rabbitt, j.C., Amer. Min., 1948, vol. 33, p. 263. [M.A. 10-416.]Google Scholar

page 711 note 1 Trace implies that the element is present, but below the limit of quantitative determination.

page 712 note 1 Heddle, M.F., Min. Mag., 1882, vol. 4, p. 213.Google Scholar

page 712 note 2 Lacroix, A., Bull. Soc. Min. France, 1888, vol 9, p. 7 Google Scholar.

page 712 note 3 E S. Dana, Syst. Min., 6th edn., 1892, p. 384.

page 712 note 4 Heddle, M. F., Min. Scotland, 1901, vol. 2, p. 40 Google Scholar.

page 712 note 5 Hey, M.H., Min. Mag., 1954, vol. 30, p. 481.CrossRefGoogle Scholar assuming the following possible errors in the chemical analysis: SiO2 0“3 %; AlsOa and H∼O 0-2 %; MgO 0.15 %; total iron as FeeOa, FeO, and Na20 0.10 %; TiO2, CaO, and K20 0.05 %; MnO %.

page 713 note 1 In fact, to regard HsO§ as an impurity, rather than essential, will almost invariably increase the apparent oxygen atoms per unit cell in any nfineral. More specifically, it will do so whenever the percentage of oxygen in the mineral is greater than 88/(D + 1), where Dis the density of the mineral. Or, if molecular ratios are calculated in the usual way by division of the percentages of the several oxides by their molecular weights, and an oxygen ratio Rois derived from the molecular ratios, interpretation of H20 + as an impurity will increase the apparent oxygen atoms per unit cell if Ro >5-51/(D+1).

page 713 note 2 McConnell, D., Amer. Min., 1950, vol. 35, p. 166.Google Scholar[M.A. 11-220]; Clay Minerals Bull., 1951, vol. 1, p. 179.