90 PHYSIOGRAPHY. 



177 35', of s on s (over M) = 91, BROOKE ; 



= 93 45' nearly, BREWSTER. 

 Cleavage, parallel to T and M, the first a little 



more distinct ; also parallel to s. Fracture small 



conchoidal, uneven. Surface s striated parallel 



to the edges of combination with M and T ; the 



remaining faces smooth. 

 Lustre vitreous. Colour white. Streak white. 



Transparent . . .semi-transparent. 

 Hardness = 5-0 ... 5-5. 



Beiore the blowpipe it gives nearly the same results as 

 other species of the genus Kouph one-spar. It first gives 

 off water, intumesces a little, and becomes opake, then it 

 melts imperfectly into a vesicular glass. The globule ob- 

 tained with borax is transparent, but vesicular ; that with 

 salt of phosphorus contains a skeleton of silica, and becomes 

 opake on cooling. With a little soda it melts imperfectly, 

 but with a larger quantity it becomes infusible. The glass 

 with solution of cobalt is dirty blueish-grey. According to 

 Dr BREWSTER, it forms a gelatine if exposed in the state of 

 powder to the action of nitric acid. 



It occurs in the cavities of an amygdaloidal rock, along 

 with paratomous Kouphone-spar, and has been hitherto 

 found only at Mount Vesuvius. The name of Comptonite, 

 given to this species by Dr BREWSTER, was proposed by 

 Mr ALLAN. 



CRONSTEDTITE. 



Cronstedtit. STEINMANN. Schweigger's Journal. Neue 

 JReihe. T. II. S. 69. Cronstedtite. PHILL. p. 227. 



Rhonibohedral. R CD. R -f oo. Reniform, mas- 

 sive : composition columnar. 

 Cleavage, R x perfect ; R 4- oo imperfect, 



