

ORIGIN OF THE CORUNDUM. 209 



our observations go at Sivamalai then the distribution of the corundum 

 is in agreement with the results indicated by Morozewicz's experi- 

 ments. But we want many more instances of the kind before we 

 can state that in Nature corundum can be formed only in magmas 

 which satisfy the conditions experimentally indicated by Morozewicz. 

 The details hitherto published concerning the Ontario occurrence are 

 insufficient as a test of Morozewicz's law. The greater abundance 

 of the corundum in the ordinary syenite, as mentioned by Miller 

 and by Coleman, are in agreement, so far as they go ; but we want 

 to know also the molecular ratio of the alumina to the other bases 

 in each case, and whether magnesia and ferrous oxide are present 

 in available quantities in excess to form spinel. In the case of the 

 felspar-rock near Sivamalai a certain amount of the alumina has been 

 used to form accessory zinc-spinel (automolite) and chrysoberyl 

 (BeO, Ai 2 O s ). 



One reason for raising the question of the universal applicability 

 of Morozewicz's law is the occurrence of corundum with peridotites 

 in North Carolina, where, according to Dr. J. H. Pratt, the condi- 

 tions point to the corundum having separated as an early-formed 

 constituent from the peridotite magma. 1 Dr. Pratt states that v 

 Morozewicz has shown that molten magmas having a composition 

 approximately that of basic magnesian rocks readily dissolve alu- 

 mina, which separates out on cooling as corundum. 2 I am unable 

 to see that any of the magmas from which Morozewicz obtained 

 corundum bear any chemical resemblance to basic magnesian rocks. 

 On the contrary, Morozewicz has pointed out that the formation of 

 corundum is independent of the basicity, whilst, when magnesia is 

 present, corundum is formed only when there is more than enough 



1 J. H. Pratt : Cn the origin of the Corundum associated with the Peridotite 

 in North Carolina. Amer. Journ. Sci. (4), VI, 1898, 49—65. 



* Op* cit. f p. 60, and in a further communication, "On the separation of 

 Alumina from molten magmas, and the formation of Corundum." Ibid. (4), VIII, 

 1899* 230. 



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