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XVIII.—The Glenboig Fireclay*

Published online by Cambridge University Press:  15 September 2014

J. W. Gregory
J. W. Gregory
Affiliation:
University of Glasgow
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According to Percy's definition, “clays are termed fireclays or refractory clays when they resist exposure to a high temperature without melting or becoming in a sensible degree soft and pasty.” The refractoriness of fireclay is due to its low proportions of fluxes. The best known British fireclays occur beneath the coal seams of the coal measures, and are therefore known as “under-clays” or “seat-clays.” The explanation of their paucity of fluxes usually offered is that the alkalies have been withdrawn as food by the vegetation which formed the coal. Thus Professor Tarr remarks that fireclays “are particularly abundant in the Carboniferous rocks associated with coal beds, the plants having been instrumental in the withdrawal of the alkalies.” This view has been widely accepted, and the death of the successive coal forests has been attributed to the exhaustion of the plant foods in the underlying soils. Caution is, however, necessary in the application of this theory; for plants can only withdraw soluble alkalies from the soil, and the alkalies are usually present in the form of silicates, which decompose slowly. Hence the total removal of alkalies from a soil by vegetation would be a very lengthy process. Moreover, alkalies are not the only, or indeed the most common of fluxes, for iron is usually the most potent. Further, some good fireclays are not associated with coal seams, while well-washed river muds may be poorer in alkali than an underclay, the alkalies having been washed out of the material. Thus the river muds from the Rhine near Bonn, analysed by Bischoff, contain only ·89 per cent. of potash and ·39 per cent. of soda; or after deducting the water and organic material the percentages of potash and soda are 1·02 and 0·45 respectively. Another analysis by Bischoff of river mud from the Rhine collected above Lake Constance contained potash ·55 per cent. and soda ·54 per cent., or after deducting the water and carbonates the percentage of these two constituents only rose to ·91 per cent. of potash and ·90 per cent. of soda.

Type
Proceedings
Information
Proceedings of the Royal Society of Edinburgh , Volume 30 , 1910 , pp. 348 - 360
Copyright
Copyright © Royal Society of Edinburgh 1910

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Footnotes

*

I must express my indebtedness for help during several visits to Glenboig to the late A. H. Dunnachie, the General Manager of Glenboig Union Fireclay Co. Ltd.; Mr J. Macintyre, the mine manager; also to Mr G. W. Tyrrell of the Glasgow University for the preparation of slides and determination of the specific gravity, and to Mr D. P. Macdonald, the Baxter Demonstrator in Geology, for the analysis of the sideroplesite. Also to Professor A. C. Seward of Cambridge and Dr J. W. Evans of the Imperial Institute for examining one of the slides, and to Mr Fingland for the photographs.

References

page 348 note † Percy, J., Metallurgy, Fuels, 1875, p. 87.Google Scholar

page 348 note ‡ Tarr, R. S., Economic Geology of the United States, with Briefer Mention of Foreign Mineral Products, 1894, p. 400.Google Scholar

page 349 note * Bischoff, F., Elements of Chemical and Physical Geology, vol. i., 1854, p. 123.Google Scholar

page 349 note † Ries, H., Clays, 1906, p. 179.Google Scholar

page 349 note ‡ Green, A. H. and others, “The Geology of the Yorkshire Coalfield,” Mem. Geol. Surv., 1878, p. 19.Google Scholar

page 350 note * Professor Boyd Dawkins, on the other hand, has identified some markings as casts of rootlets; the evidence for this identification seems to me, however, inadequate.

page 350 note † Summary of Progress of the Geological Survey for 1905 (pp. 119–121) and for 1907 (pp. 102–103).

page 351 note * See, e.g., A. H. Green, op. cit., p. 19.

page 352 note * Liversidge, A., Minerals of New South Wales, 1888, p. 195.Google Scholar

page 352 note † Dana, , System of Mineralogy, 6th edit., 1892, pp. 688–689.Google Scholar

page 353 note * Green, A. H., Physical Geology, 1876, p. 68.Google Scholar

page 354 note * Reusch, H., “Krystallinische Kaolin von Denver in Colorado,” Neu. Jahrb., 1887, vol. ii. p. 71.Google Scholar

page 354 note † Hutchings, W. M., “Notes on the Probable Origin of some Slates,” Geol. Mag., New Ser., decade 3, vol. vii., 1890, p. 271.Google Scholar

page 354 note ‡ The publication of this paper has been delayed to allow some chemical tests as to the solubility of the clay substance to be repeated. According to Lacroix kaolinite is “inattaquable par les acides,” while hydrochloric acid “décompose facilement” halloysite. This distinction between the two species seems reasonable, as an amorphous material such as halloysite might be expected to be more easily decomposed than a crystalline species such as kaolinite. A careful investigation by Mr D. P. Macdonald shows that the clay substance of Glenboig fireclay is readily decomposed by boiling in hydrochloric acid. Thus 6·5 per cent, of the total of 37·65 per cent, of alumina was dissolved out by boiling for two hours in hydrochloric acid, 23·2 per cent, by boiling for six hours, and practically the whole of it (36·6 per cent, out of 37·65 per cent.) by boiling for thirteen hours. Boiling in hydrochloric acid therefore completely decomposes the material; and if M. Lacroix's distinction be valid, it cannot be kaolinite.

As the Glenboig fireclay is of Carboniferous age and underlies an intrusive sill, it is not surprising that the percentage of water in its clay substance is smaller than in some of the more recent French halloysites, and it is therefore somewhat less readily decomposed and is nearer in physical properties to kaolinite than varieties of halloysite with a higher percentage of water.

page 354 note § Hatch, F. G., Text-book of Petrology, 1892, p. 103.Google Scholar

page 354 note * Minéralogie de la France et de ses Colonies, vol. i., Paris, 1895, p. 472.

page 355 note * This identification was subsequently fully confirmed by MrHickling, G., “China Clay; its Nature and Origin,” Trans. Fed. Inst. Min. Eng., vol. xxxvi., 1909, pp. 1–26, pl. 1.Google Scholar

page 355 note † For the presence of quartz flour as a clay constituent, see, e.g., Senft, F., Die Thonsubstanzen, Berlin, 1879 (published 1878), p. 15.Google Scholar

page 355 note ‡ F. Senft, ibid., p. 16.

page 355 note § Hutchings, W. M., “Clays, Shales, and Slates,” Geol. Mag., decade 4, vol. iii., 1896, p. 315.Google Scholar

page 356 note * Karpinsky, A., “Die Trochilisken,” Mém. Comité Géol., new ser., No. xxvii., St Petersburg, 1906, viii + 172 pp.Google Scholar; 3 pl., 59 figs, (in Russian, with German summary); see, e.g., fig. 7, p. 12; fig. 10, p. 18; fig. 74, p. 82; and pl. 3, fig. 2.

page 356 note † Fakes is a local term for laminated sandy clay or sandy shale.

page 357 note * Breithaupt, A., “Beschreibung neuer Mineralien,” Berg- und huttenm.-Zeit., vol. xvii., 1858, p. 54.Google Scholar

page 357 note † Louis, H., “On the Ankerite Veins of Londonderry, Nova Scotia,” Trans. Nova Scotta Inst. Nat. Sci., vol. v., 1882, pp. 47–53.Google Scholar

page 358 note * ibid., p. 50.

page 358 note † ibid., p. 52.

page 358 note ‡ Heddle, M. F., Mineralogy of Scotland, vol. i., 1901, p. 141.Google Scholar

page 359 note * Cullis, C. G., “On a Peculiarity in the Mineralogioal Constitution of the Keuper Marl,” Rep. Brit. Assoc. Leicester, 1907, p. 507.Google Scholar

page 359 note † Summary of Progress, 1907, p. 103.