WATSON AND STEIGER: SPINELLITE FROM VIRGINIA 669 



yielding varicolored residual clays, chiefly pink to deep red and 

 brown, in which the structure of the original schists is usually 

 completely preserved. The ore bodies have a general north- 

 easterly strike, with steep dips to the southeast which frequently 

 approach the vertical. In the thin stringer-like bodies, closely 

 spaced and alternating with thin bands of schist, many speci- 

 mens exhibit beautiful folds. Chlorite is similarly associated 

 with the ore bodies formed in the schist as with those formed in 

 the granite described above. Marked contact effects on the 

 schist are shown in places, involving the development of an en- 

 tirely new set of minerals, including sillimanite and some andalu- 

 site w4th the ore minerals, spinel and magnetite, and in places a 

 little corundum. 



PETROGRAPHY OF THE EMERY. 



The rock emery is a heavy black fine-grained crystalline ag- 

 gregate that resembles somewhat closely a homogeneous fine- 

 grained magnetite ore. It is an exceedingly tough rock and is 

 magnetic from the presence of magnetite as one of its constitu- 

 ents. A small horseshoe magnet wdll pick up very small frag- 

 ments of the ore but will usually not lift pieces a half inch or 

 more in size. The texture of the ore may or may not be entirely 

 uniform. More often it is uniform but frequently difference in 

 granularity (size of grain) even in a small hand specimen is 

 emphasized by sharp usually parallel boundaries which impart 

 a distinct banded appearance to the ore. This difference in granu- 

 larity seems to be more frequent in the ore in schist than in the 

 ore in granite, but it occurs in both. In the coarsest textured 

 emery the mineral grains do not exceed 2 mm. in diameter, 

 while in the finer textured rock, which includes most of the ore, 

 they are under 0.1 mm. 



In the most of the ore none of the component minerals can 

 be distinguished by the naked eye. In the schist occurrences, 

 however, the ore contains corundum sufficiently coarse to be 

 readily identified on sight, formed usually in small segregation- 

 like areas or bunches or as thin light-colored bands or streaks. 



