382 



Review of Dana's Mineralogy. 



Fig. 18. 



Mi 



" Primary form, an oblique rhombic or rhomboidal prism ; M : T= 

 110° to 98°, crystals having the faces M smooth and plain, give the 

 latter, which therefore appears to be the correct 

 angle of the prism. Seeondary form, the annexed 

 figure ; P : M=105°, P : e=133° 30', M : e=:120° 

 30', P : a=\32°, (D.) The terminal planes dull 

 and hardly smooth. Cleavage highly perfect, par- 

 allel to the longer diagonal, and producing brilliant 

 surfaces ; parallel to M indistinct. Crystals usually 

 long and slender. Occurs also long fibrous, paral- 

 lel, or slightly divergent. 



« H.=7— 7-5. G.=3-2— 3-238, D. ; 3-259, Norton. (Yorktown.) 

 Lustre vitreous, inclining to pearly ; hardly shining on M, but splendent 

 on the face of perfect cleavage ; parallel to P, vitreous, inclining to re- 

 sinous. Streak white. Color hair-brown — grayish-brown. Translu- 

 cent. Fracture uneven, parallel to P. Brittle. The long crystals are 

 detached from the rock entire, with great difficulty, on account of their 

 frangibility. 



"Composition, according to Bowen, (Sill. Jour, viii, 113,) Muir, 

 (Thorn. Min. I, 424,) Connell, (Jameson's Jour, xxxi, 232,) and Nor- 

 ton, performed for this work, in the laboratory of B. Silliman, Jr. 



99-286, B. 99-502, M. 96-68, C. 102-739, N. 



" The analyses by Connell and Norton show that this mineral con- 

 tains no Zirconia. 



" Before the blowpipe, both per se and with borax it is infusible. 



u Obs. The crystal here figured appears to have dissimilar lustre on 

 M and T, and this, as well as the secondary planes, indicates that the 

 primary is probably a rhomboidal prism. In composition, Sillimanite is 

 very close to Kyanite, if they are not identical ; yet its bright and easy 

 cleavage shows that it is mineralogically distinct from that species." 

 (pp. 377, 378,) 



Connell proposed (Jameson's Jour., Vol. xxxi, p. 232) the union 

 of Sillimanite with Kyanite, and Berzeliusf in his report for this 



* Chester, Ct. is quoted in Thomson and other foreign authors as Saybrook, Ct. 

 t Arsbert e Kemi och Min. (Swedish edition,) 1843, p. 202. 



