

ORIGIN OF THE CORUNDUM. 



211 



lustrous mineral undetermined. The " corundum-syenite " forms 

 stocks of a medium-grained, granular structure and pink colour 

 composed of corundum, orthoclase and microperthite, biotite and 

 some secondary muscovite. The rocks gave the following results 

 on chemical analysis :— 





I. 



la. 



II. 



Ua. 



III. 



Corundum 



35*40 



— 



1855 



— 



— 



SiO a 



. 40*06 



6271 



523+ 



64-65 



63-68 



A1 2 3 . 



i3'65 



21*37 



16-05 



I9-83 



2060 



Fe a 3 . 



0-35 



0*55 



o*45 



056 



o-55 



CaO 



030 



o'47 



0'20 



025 



036 



MgO . 



015 



0-23 



o'i6 



019 



021 



K a O 



5' 20 



8-14 



6-58 



8-14 



8-14 



Na a O . 



3*7i 



5-8i 



477 



5-89 



5*85 



Water . 



0*46 



072 



0*40 



0-49 



061 



99*28 ioo'oo 99*50 IOO'OO IOO'OO 



I.— Corundum-(syenite)-pegmatite. 

 II. — Corundum-syenite of Nikolskaja Ssopka. 



III. — Average of the two analyses adjusted to 100 after deduct- 

 ing the corundum. 



Deducting the corundum from I and II and calculating the 

 remainder to 100, we obtain the figures given in columns la and Ua, 

 respectively, of which the average, III, agrees very nearly with the 

 composition of the felspar-rock containing corundum near Sivamalai. 

 Morozewicz calls attention to the fact that the molecular value for 

 soda exceeds that for potash, which is an important circumstance, 

 as he finds that, although alumina is readily soluble in molten soda- 

 alumino'silicate, it is insoluble in potash-alumino-silicate, whilst the 

 introduction of soda into the latter rapidly increases its solubility 

 which is of course an essential preliminary to its subsequent separa- 

 tion in crystal form. The same remark applies to the corundiferous 

 felspar-rock near Sivamalai, in which the soda also exceeds the 

 potash in quantity and in molecular proportion, the ratio being 

 Na 2 : KoO =5 : 1 (see p. 35). 



( 43 ) 



