WATSON AND STEIGER: SPINELLITE FROM VIRGINIA 



675 



percentages of TiO: in the analyses — a constituent not reported 

 in the analyses of the Naxos emery. 



Pleonaste, corundum, and magnetite with some ilmenite are 

 the principal minerals in the emery from Virginia and New York, 

 while magnetite and conmdum are the components of the Naxos 

 emery, with little or no spinel and ilmenite. The wide varia- 

 tion in the principal constituents shown in the two analyses of 

 the Peekskill emery is due directly to difference in the proportion 

 of the same minerals as expressed in the modes determined by 

 Rogers." Omitting the less than 2 per cent of quartz, the mode 

 in each case as given by Rogers is shown in table 4. 



TABLE 4 



Modes of Peekskill, New York, Emery (Rogers) 



Spinel 



Corundum. 

 Magnetite. 

 Ilmenite. . . 



» Corresponds to same number in table 3. 



The same minerals are shown above to be the chief compo- 

 nents of the Virginia emery, but the spinel in excess of the other 

 minerals, is shown to differ from that of the Peekskill emery in 

 that re203 isomorphous with AI2O3 enters largely into its com- 

 position. A^ariation in the mineral proportions is likewise an 

 important factor in explanation of the differences shown in the 

 analj'ses of the emery from New York and Virginia. 



The norm of the Virginia rock calculated by Washington from 

 analj^sis I in table 3 is: 



Norm of Virginia emery 



Corundum 45 . 09 



Nephelite 0.85 



Olivine 6.38 



Magnetite 33.87 



Ilmenite . 99 



(Mg, Fe)0 5.71 



Rest 1.48 



* Rogers, G. S., op. cit., p. 64. 



