186 MR. A. K. COOMAKA-SWAMY ON THE OCCTJEEENCE [May I9OI, 



to r (1011) is not infrequent ; the cleavage-cracks become more 

 conspicuous in polarized light, as is often the case with calcite. 

 Traces of a parting parallel to c (0001) are also sometimes seen. 

 The rock appears a little bleached in the neighbourhood of the 

 corundum, that is, colourless minerals rather than mica are usually 

 in contact with it ; but this is not invariably the case. Less pure 

 corundum occurs also in a finely granular form, mixed with other 

 minerals from which it has not, as it were, been able to free itself. 

 Isolated crystals, detached from the matrix, and washed in hot 

 hydrofluoric acid, are tabular in form, being combinations of the 

 hexagonal prism and basal plane, the latter characteristically striated 



Fig. 2. — Three individuals of corundum seen in a thin section of 

 one of the included fragments. 



f^On the left hand is one with hexagonal outline, cut approximately parallel 

 with the hasal plane. A zone of lighter coloured minerals separates the 

 three crystals from the darker part of the rock. From a photograph : 

 X 27-5.] 



(see fig. 1, p. 185) and sometimes slightly stepped. One of the 

 largest measured about 1-7 mm. in greatest diameter by '5 mm. in 

 thickness, and weighed about -005 gramme. The crystals have a 

 beautiful sapphire-blue colour. 



The dark mica is strongly pleochroic, from warm dark-brown to 

 pale straw-colour. 



Andalusite is fairly common, occasionally showing faint charac-i 

 teristic pleochroism, or nearly rectangular cleavage with diagonal] 

 extinction. The greater part is, however, ill-defined, and not easy' 

 to distinguish. 



