348 A. K. Coomdrasivdmy — Contributions to Ceylon Geology. 



Y. — Contributions to Ceylon Geology: 

 Occurrence of Corundum in situ near Kandy, Ceylon. 



By A. K. CooMARAswAMY, B.Sc, P.L.S., F.G.S., Director of the Mineral Survey 



of Ceylon. 



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 situ ; 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. Iviii, pi. 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 7-3^ 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. The corundiferous band is about three yards from the 

 northern boundary of a band of crystalline limestone about seven 

 yards wide (in the lower part of the pit the distance was apparently- 

 less). There is nothing to suggest any connection between the 

 occurrences of corundum and limestone. It is a little strange that 

 corundum has not so far been found in the crystalline limestones of 

 Ceylon, although so characteristic of similar rocks in Burmah. 



The sapphii'es are of fair size, the largest about three quarters of 

 an inch in diameter, and though of a bright blue colour, are useless 

 as gems owing to their opacity and well-developed cleavage, and 

 often weathered, bleached, and hydrated condition. Ehombohedral 

 cleavage and a basal parting are alike well displayed. Combinations 

 of the hexagonal prism and basal plane are most usual, giving 



a columnar aspect ; the forms observed include c (0001), a (1120), 



r (1011),}* (2243); some double crystals with basal planes inclined at 



1 It is very usual for the grauulitic 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 haolinization of the 

 felspars, 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. 



