390 



[August IS, 



0.80 

 8.80 

 4.15 



dl 



3.004 



32..") 



48.87 



0.00 



0.23 



10.48 



trace 



2.38 



0.43 



4.34 



(32 



33.10 

 52.20 

 trace 



8.44 

 trace 

 2.59 



4.85 



99.04 



101.18 



'>. Corundum, altered into FlbroUtc. 

 a. In my previous paper I mention an observation by Prof. C. 



Sliepard tliat at the Falls of the Yantic near Norwich, Conn., small 

 crj^stals of sapphire are completely surrounded by fibrolite. Since then, 

 Pi"of George J. Brush has kindly presented to me a specimen which 

 is quite interesting. It is a fibrolite of a brownish-white color, and shows, 

 if examined with a strong lens, disseminated through the mass, numerous 

 particles or remnants of grayish-blue corundum from which the fibrolite 

 Avas formed ; but besides, there is implanted in the fibrolite, a small hexa- 

 gonal crystal of brown corundum 5'""^ long and 1.5™" thick, which 

 must have crystallized at the time when the fibrolite was formed. 



b. Recently this rare alteration of corundum into fibrolite has been 

 found in numerous specimens at Shoup's Ford, Burke Co., X. C. 



The corundum occurs in a mica schist in crystals, varjMng generally 

 between 20 and 75""™ in length and from 10 to 45"™ in thickness, it has 

 a brown or a bronze color and many crystals exhibit a star of six rays. 

 The crystals are frequently flattened, always altered on the surface, rarely 

 to a depth of 5""°. The alteration consists of an aureole of very fine 

 fibrous and radiating white fibrolite. 



It seems that subsequently the fibrolite underwent a partial alteration 

 into mica, as the mica schist in which the crj'^stals are imbedded contains 

 stili a large admixture of fibrolite. 



c. I have very little doubt that the alteration, described by Sillem 

 (Jahrb. fiir Mineralogie, 1851, 385), of corundum into ywarfo from Barsovka 

 in the Ural is really that into fibrolite. 



The altered mineral surrounds a core of unchanged corundum from 

 which it radiates. 



My opinion is supported by the fact that Sillem's description of this 

 alteration is identical with mine of corundum into fibrolite ; then, that 

 quartz very rarely assumes a radiating structure ; that fibrolite has nearly 

 the hardness of quartz ; and finally that his statement is not supported by 

 an analvsis. 



