Troost on the Pyroxene. 63 



is found in the Basalt of the neighbourhood of Cologne, 

 seems to belong to this variety. The properties of this 

 substance differ much from the former ; it is amorphous, 

 black with a tinge of green and a resinous lustre — it is 

 opaque, or sometimes slightly translucent. Its sp. gr. is 

 •2.666. It melts with intumescence before the blow-pipe, 

 into a black or brown glass. According to Klaproth it 

 contains 



9S.50 



It is this analysis which has given it a place in the 

 Pyroxexe family. It is besides found in the form of 

 small fragments in a bed of Carb. of Lime at Ginliana in 

 Sicily. Dolomieu found it in Val di Xoto of a greyish 

 green or brownish colour. 



4. Altered Volcanic P. This Pyroxexe offers three 

 modes of alteration, which it is of interest to point out. 

 When the lavas have been exposed a long time to the ac- 

 tion of the sulphureous acid vapours, which rise continu- 

 ally from the solfutara and the craters of the volcanos, their 

 nature is changed, and this is also the case with the Py- 

 roxexe which is imbeded in these lavas. The Pyrox- 

 ene becomes opaque, white, and the constituent parts, 

 with exception of the Silex, enter into combination 

 with the acid vapours, forming soluble salts, which arc 



