70 ANNALS NEW YORE ACADEMY OF SCIENCES 



tered through the rock, usually associated with the more basic minerals; 

 it is generally of the typical colorless variety, occurring in medium-sized 

 idiomorphic crystals. In ore from certain places, however, the corundum 

 is deep bluish green in color, resembling glaucophane, with strong pleo- 

 chroism: E light greenish yellow, and dark greenish blue. It then 

 occurs in stouter crystals, with less distinct outline. Once recognized as 

 corundum, it is always unmistakable. Spinel is typical and abundant, as 

 is also magnetite. Sillimanite, in long blades and in a confused fibrous 

 mass (fibrolite), is often present. 



Quartz-Emery Schist 



Quartz-emery schist is most closely associated with the last variety, 

 which grades into it ; it is also, however, found in the spinel emery mines. 

 It is usually consigned to the dump as too poor in emery. Quartz streaks 

 run through it in great abundance and give it a distinctly gneissoid ap- 

 pearance, and it was this resemblance to a schist or gneiss which first 

 suggested (to Dr. Berkey and the writer independently) that it might 

 possibly be an altered inclusion. This texture is brought out to a certain 

 degree in the accompanying photograph of a typical hand specimen 

 (Plate V, fig. 2). It is much like the feldspathic emery under the micro- 

 scope, differing chiefly in the abundance of quartz. This is in large inter- 

 locking grains, and it may compose one third or more of the rock. It 

 sometimes carries an abundance of rutile inclusions in sharp yellowish 

 needles. The corundum in this rock is often of the peculiar variety de- 

 scribed under the last; and the rock may (at the Buckbee mine for ex- 

 ample) become very sillimanitic. 



Besides these distinct varieties of ore, corundum or spinel, or both, 

 may occur in the wall rocks, such as diorite, norite, etc. In these rocks, 

 the corundum is usually in more irregular crystals, and the common 

 colorless variety may show pleochroic blotches of an ultramarine blue. 



Norite Proper 



While norite proper must bear the same name as that given the more 

 widely spread variety, it is in reality a somewhat different rock. In the 

 hand specimen, it usually is of a soft brownish color, being apparently 

 composed of enstatite and feldspar, with the former generally in excess. 

 The rock is perfectly massive. In thin section, the dark mineral is seen 

 to be orthorhombic pyroxene of a peculiar type. It is usually more or 

 less idiomorphic, occurring in rounded oblong crystals, a habit not seen 

 in typical norite. The pleochroism is weak ( X yellowish pink, Z grayish 



