WATSON AND STEIGER! SPINELLITE FROM VIRGINIA 667 



scales of biotite sparsely scattered through it. The ore bodies 

 are associated with the aplite-pegmatite and not with the 

 granitite. 



The granite aplite-pegmatite is a white muscovite-bearing rock 

 which exhibits the usual irregularities of texture of such rocks. 

 Chemical analyses, as would be expected, show it to be distinctly 

 more silicic than the granitite. Microscopic study of thin sec- 

 tions shows the principal minerals to be quartz and feldspar 

 (orthoclase and albite in varying proportions) with some 

 muscovite. 



The chemical composition of the granite aplite-pegmatite is 

 shown in table 1 below in the average of three analyses of samples 

 collected from different parts of the area. 



TABLE 1 



Average of Three Analyses of Granite Aplite-Pegmatite, Pittsylvania 

 County, Virginia. (S. D. Gooch, Analyst) 



Per cent 



SiOs ■ 76. 19 



AI2O3 15. 14 



FeaOs 66 



FeO 19 



MgO ^ trace 



CaO ' 47 



NaoO 4.16 



K:0 2.29 



H2O- 05 



H,0+ 1.06 



TiOj 02 



P2O5 11 



MnO 02 



CO2 none 



100.36 

 Sp.Gr 2.671'' 



" Average of three determinations on separate rock fragments, ranging from 

 2.659 to 2.693. 



Calculated in the usual way, the principal normative compo- 

 sition of the rock corresponding to the above analysis is : 



Quartz 41.9 



Orthoclase 13.3 



Albite 35. 6 



Anorthite 2.5 



