154 PHYSIOGRAPHY. 



town of Saybrook, Connecticut, and was formerly consider- 

 ed as a variety of Anthopyllite. The analysis agrees ex- 

 actly with that of prismatic Disthene-spar by KLAPROTH, 

 (Vol. II. p. 215.). No exact crystallographic description is 

 given, but the angle of 106 30' is very near the incidence of 

 P on M, 106 15', in that species, also the specific gravity is 

 not much different, and the great hardness may perhaps 

 be accounted for by the want of a more general diffusion of 

 correct methods for ascertaining this property. Sillimanite is 

 therefore probably a variety of the prismatic Disthene-spar. 



SOMERVILLITE. 



Somervillite. BROOKE. Brande's Quarterly Journal. Vol. 

 XVI. p. 274. 



Pyramidal. P = 134 48', 65 5(K Vol. I. Fig. 8. 

 BROOKE. 



a = V 0-419. 

 Simple forms. P co (P) ; P (a) ; P + o> (d) ; 



[P 4. a,] (M) ; (P + oo) 3 (e) = 126 52' 12", 



143 7 48". 

 Combination of all these forms, resembling Fig. 101 ., 



having the apex, and the edges between g and 



I replaced. 

 Cleavage, P GO perfect, none observable parallel 



to the axis. 

 Lustre more glassy in the cross fracture than that 



of pyramidal Garnet. Colour pale dull yellow. 

 Hardness inferior to that of pyramidal Garnet. 



It decrepitates before the blowpipe, and melts alone into 

 a grey coloured globule, with borax into a colourless one. 

 It occurs at Mount Vesuvius, associated with black mica 

 and other minerals. 



