( ^^ ) 



cliaracter of '• star sapphires " isMue to the presence of regularly 

 distributed minute inclusions arranged along the lines oi" growth, 

 producing the appearance known as " silk ;" a six-rayed star is 

 seen when the crystal is viewed iji the direction of its vertical axis. 

 Coarser varieties of coruiulum are used as emery, for which pur- 

 pose a good deal is obtained in Southern India. Corundum is 

 found in the river gravels of Ceylon in more or less rounded and 

 waterworn six-sided crystals, which are either prismatic or doubly 

 pyramidal in character. 



Only two localities are known in Ceylon where corundum 

 occurs in the parent rock. In one case (Talatu-oya) blue hexa- 

 gonal crystals occurred in a narrow band of rock composed essen- 

 tially of orthoclase, microperthite, and oligoclase. In the other 

 (Haklunimulla) violet or purplish hexagonal crystals are found 

 in a corundum-sillimanite rock (of which a large specimen is 

 exhibited), but not actually in situ. 



In Southern India corundum occurs {a) in felspathic rocks as a 

 direct product of the magma ; {h) in certain aluminous rocks, 

 probably as the result of contact metamorphism. Specimens of 

 these rocks are shown in the collection. In Burma rubies are 

 found in the crystalline limestones, which in other respects 

 closely resemble those of Ceylon. 



Hematits, FegOg, — Less usual than limonite as an iron ore 

 derived from the decomposition of the granulitic rocks. 



Limonite, 2Feo033H20. — The common ore of iron in Ceylon, 

 and formerly extensively worked. Almost always found as a 

 proilact of the decomposition of the granulites. 



HydrargilUte, AI2O33H0O. — Forms, with limonite, the greater 

 part of ordinary laterite (cabook). 

 Gassiterite, SnO.,. 

 Rutile, TiO,,. 



Thorianite, ThO., +U0;,. — This newly-discovered mineral, 

 peculiar to Ceylon, is of great commercial importance owing to 

 the use of thoria in the manufacture of incandescent gas mantles. 

 It occurs in very heavy black cubic crystals at Bambarabotnwa, 

 where over a ton has been obtained. It is valued at £600 sterling 

 per ton. It is of great scientific interest too, on account of its 

 chemical composition, one or more new elements being possibly 

 present ; it contains also a large amount of occluded helium. 

 Though radio-active, there is no more than a trace of radium 

 present. 

 Baddeleyite, ZrOg. 



(^jmr^s, SiOo.— Very abundant throughout the Charnockite 

 Series. The purple variety is amethyst. Drusy grou})B from 



