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V.—Contributions to Ceylon Geology: Occurrence of Corundum In Sitû Near Kandy, Ceylon
Published online by Cambridge University Press: 01 May 2009
Extract
The present notes are based on field observations made in 1900. The section described is now obscured.
Corundum is abundant in the gem-bearing gravels of Ceylon, but with the exception of the case here described no localities are known where it occurs in sitû; the present occurrence is therefore of considerable interest, although not very satisfactory in itself.
Crystals of corundum were found in the surface soil on a piece of land known as Tenna Hena, and situated east of Kandy, and three-quarters of a mile north-east of Talatnoya bridge. The exact spot is shown in a map accompanying a paper on the crystalline limestones of Ceylon (Quart. Journ. Geol. Soc, 1903, vol. lviii, pl. xiii). A small excavation had been made, and a few pounds of corundum extracted and sold for use as emery, before my visit to the spot. All the rock exposed was decomposed, and crumbled in the fingers, being in a condition resembling sand. I therefore carried on an excavation for two months, hoping to reach hard rock suitable for microscopic examination, but although a depth of about 30 feet was reached, no sufficiently hard rock was found.
At the corundum pit the ‘beds’ of granulite dip northwards at a high angle. A conspicuous soft yellow micaceous band 7–3½ inches wide marks the position of the sapphire-bearing zone. The sapphires occur in fair abundance in a less decomposed felspathic rock occupying a few inches on either side of this yellow micaceous band in the upper part of the shaft, but on the south side only in the lower part. The associated types of granulite are chiefly acid leptynite.
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References
page 348 note 1 It is very usual for the granulitie rocks of Ceylon to be found in this friable, sandy condition, to a considerable depth. This mode of alteration is totally distinct from the formation of laterite, nor does it appear to be due to the kaolinization of the felspar, as these are translucent, and the analysis shows that but little water is present. The change partakes perhaps rather of the nature of a physical disintegration.
page 349 note 1 The presence of free quartz would raise the amount of available excess alumina, as indicated by the chemical analysis. After careful microscopie examination, however, I feel that there can hardly be any appreciable quantity of free quartz present, if any.
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