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IV.—On the Constitution, Origin and Dehydration of Laterite

Published online by Cambridge University Press:  01 May 2009

T. H. Holland
T. H. Holland
Affiliation:
Geological Survey of India.
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Extract

The objects of this note are three: (1) to call attention to the essential chemical similarity between laterite and bauxite; (2) to offer a theory for the formation of laterite in the moist tropics; (3) to suggest an explanation for its spontaneous dehydration.

(1) Laterite has generally been referred to as a ferruginous clay; but if the term clay is restricted to substances having a basis of hydrous silicate of alumina, this definition is incorrect. The alumina in laterite exists, as it does in bauxite, in the form, of hydrous oxides. Kaolin must thus be removed finally from the list of weathering products; it is formed generally, perhaps exclusively, by the action of subterranean vapours on aluminous silicates. This conclusion necessitates a re-examination of many so-called argillaceous substances; many doubtless include the kaolin already existing in the kaolinized aluminous silicates before they are exposed to the weather. But it is probable that some of the red clays of past geological ages, formed under subaerial conditions, contain free hydrous oxides of alumina; and for those that are shown to contain hydrous silicate of alumina, it would be well to test the possibility of a secondary reunion of aluminic hydrate and free silicic acid.

(2) To account for the fact that an aluminous silicate undergoes a more complete disintegration under tropical conditions than under the deep-seated and presumably high-temperature conditions of kaolinization, the writer suggests that laterite is due to the agency of lowly organisms, possibly akin to the so-called nitrifying bacteria.

Type
Original Articles
Information
Geological Magazine , Volume 10 , Issue 2 , February 1903 , pp. 59 - 69
Copyright
Copyright © Cambridge University Press 1903

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References

page 59 note 1 Bauer, , “Beiträge zur Geologic der Seychellen”: Neues Jahrb. für Min., etc., 1898, vol. ii, p. 163.Google Scholar

page 59 note 2 Cf.Henatsch, , “Ueber Bauxite und ihre Verarbeitung”: Iuaug. Dissertation, Breslau, 1879.Google Scholar Mr. F. R. Mallet, to whom I am indebted for reading the proofs of this note during my absence from England, approached dangerously near comparing laterite with bauxite when he pointed out in 1881 that the ferruginous beds of Ulster, associated with bauxite, resembled the laterite on the Deccan Trap in India. (“On the ferruginous beds associated with basaltic rocks of North-Eastern Ulster, in relation to Indian laterite”: Rec. Geol. Surv. Ind., vol. xiv, p. 139.)

page 59 note 3 Holland, , “A Contribution to the Discussion on Rock-Weathering and Serpenti-nization”: Geol. Mag., 1899, Dec. IV, Vol. VI, p. 540.Google Scholar

page 60 note 1 Rösler, , “Beiträge zur Kenntniss einiger Kaolinlagerstätten”: Neues Jahrb. für Min., 1902, vol. xv, Beilage-Band, pp. 231–393.Google Scholar

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page 64 note 1 Holland, , “The Charnockite Series”: Mem. Geol. Surv. Ind., 1900, vol. xxviii, p. 197.Google Scholar

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page 65 note 1 Geol. Mag., December, 1899, p. 542, note 1.

page 66 note 1 The actual identity of results by these two equations is, of course, accidental; for it is not known that the molecular volume of Al2 O3 remains constant in all its combinations. But, for reasons that need not be stated now, it is certain that its variations in crystallized compounds is very much less than the difference between the molecules of water.

page 66 note 2 Thorpe, & Watts, , “On the Specific Volume of Water of Crystallization”: Journ. chem. Soc, 1880, vol. xxxvii, p. 102.Google Scholar

page 67 note 1 Thomsen, J.: “Thermochemische Untersuchungen,” 1882, vol. iii, pp. 240, 294.Google Scholar Roberts-Austen, : Nature, August 8th, 1901, p. 360.Google Scholar Naumann, : “Thermochimie,” 1882, p. 514.Google Scholar