94 



and the remaining constituents recalculated to a basis of 

 ioo. Under IV is an analysis of the separated microper- 

 thite from the corundurn-syenite-pegmatite of Craigmont, 

 Ont. Under V is an analysis of a similar feldspar of the 

 corundum-syenite-pegmatite from Sivamalai, India, [7, p. 

 202]. 



— 



I 



II 



III 



la. 



Ila. 



Ilia. 



IV 



V 



Corundum 



34-62 



40-53 



13-62 



o- 19 



0-04 



0-67 



35-40 



40-06 



13-65 



o-35 



18-55 

 52-34 

 16-05 



o-45 













Si0 2 



A1 2 3 



Fe2C»3 



FeO 



62-30 



20 -93 



0-29 



0-06 



I -02 



9- 10 



5-23 

 1 -07 



62-71 

 21-37 



o-55 



64-65 



19-83 



0-56 



63-43 



20-78 



0-29 



63-26 

 21-87 



0-22 



CaO 



MgO 



0-30 

 0-15 

 5- 20 



3-7i 

 0-46 



0-20 



o- 16 



6- 5 8 



4-77 

 0-40 



o-47 

 0-23 

 8-14 

 5-8i 

 0-72 



0-25 

 0-19 

 8-14 

 5-89 

 0-49 



1 -oo 

 0-07 

 8-oo 

 5-20 



1 -00 



0-21 



K 2 



Na 2 . 

 H 2 



5-92 

 3-40 



I -OI 



3-09 

 IO-25 



0-78 





IOO- 00 



99-28 



99-50 



ioo- 00 



IOO -00 



ioo- 00 



99-79 



99-68 



The frequent occurrence of corundum in the nepheline 

 syenites of Ontario gives these rocks a unique petrographical 

 position, for although similar rocks occur as differentiation 

 products of the corundum syenites of India or Russia, no 

 corundum has yet been found in these countries in varieties 

 which actually contain nepheline. 



There is no doubt whatsoever that the corundum in 

 these rocks is a true pyrogenetic mineral being clearly a 

 primary constituent which separated out of the highly 

 aluminous silicate magma as one of the first products of 

 its crystallization. 



The amount of corundum present in certain varieties 

 of these syenites is sometimes very large, thus the ordinary 

 red syenite-pegmatite of Craigmont was found to contain 

 34-14 per cent of corundum; while dungannonite from 

 the Township of Dungannon contains 13-46 per cent of 

 this mineral. As a result of the crushing and concentration 

 conducted on a large scale for a period of two years at the 

 Craigmont mill, it was found that 10 -6 per cent of corun- 

 dum was separated from the rock treated, while a small 

 portion of the mineral still remained in the tailings. 



