

Prof. B. Sillimati) Jr., on some American Minerals. 389 



Silica, 

 Alumina, 



38- 



58-25 



96-25 



Even upon so imperfect an analysis, there has been no hesita- 

 tion with most writers in referring it to kyanite. Having a speci- 

 men of this mineral from Count Bournon at my disposal, I have 

 analyzed it.* It yielded on 0*427 gramme taken: 



Silica, . . . -1551^ per ct. 36309 



Alumina, . . -2665 " 62415 



Magnesia . . -0030 " -702 



•4246 99-426 



The results just given leave it no longer possible for us to sep- 

 arate sillimanite, bucholzite and fibrolite from kyanite. The 

 hardness of sillimanite proves also to possess the same inequality 

 on different faces which is found in kyanite. The cleavage face 

 is much softer than the angle or side of the prism, so as to be 

 easily scratched with a sharp point of hard steel. The crystal- 

 line forms of sillimanite and kyanite are also identical, the one 

 being derived by the simplest modification from the other. The 

 cleavage in both is in the orthodiagonal. 



It may be worthy of remark that " Andalusite" has the same 

 chemical constitution as kyanite, but belongs to the right rhombic 

 form, while kyanite is oblique. Doubtless a case of dimorphism, 

 a nd perhaps the same may be said with truth of staurotide. 



My pupil, Mr. George J. Brush, afforded me essential aid in the 

 foregoing investigation. 



V. On a Granular Albite associated with Corundum, and on 



THE INDIANITE OF BoURNON. 



A specimen of a granular mineral was sent me by Mr. G. of 

 Andover, last year, with the remark that it was found in beds in 

 Lancaster Co., Penn., and was so hard as to resist all attempts 

 to penetrate it by hardened steel — greatly impeding the opera- 

 tions of the miners in the chrome iron districts. 



I also received other specimens of the same from Mr. Williams 

 ?f Westchester, associated with corundum which was found 

 inibeded in it, and from this circumstance it has been mistaken 

 by some mineralogists for Indianite, which species it resembles 

 M hardness, gravity and in granular structure, but not at all in 

 composition. 



* The specimen referred to was taken from the collection of Col. Oibbs , (now in 

 "le College,) and was received by him from Count Bournon in a large collection of 



mf ** wege,; ana was received by him irom i- 

 gems which this gentleman furnished to Col. G. 



Second Series, Vol. VIII, No. 24.— Nov., 1849. 



50 



