Troost on the Pyroxene. 65 



which would induce the belief that lava contained two 

 different varieties of Pyroxene, the one easily decompo- 

 .sible, and the other not, which is also the case with fel- 

 spar. 



The other state of decomposition the Pyroxene under- 

 goes, is this — it becomes green, with an earthy aspect, 

 loses its internal structure and other characters, but pre- 

 serves its form. This kind of decomposition we observe 

 particularly in transition rocks of the nature of Wacke, or 

 in those constituting the Amygdaloids, which contain the 

 Zeolite varieties. One of the most remarkable instances 

 is found in the rocks composing the Mount Pazza, in the 

 valley of Fassa Tyrol. The rock is a Wacke which con- 

 tains crystals of Pyroxene, variet. Bisunitary — thus al- 

 tered and transformed into a kind of green earth, which 

 the German mineralogists have considered sometimes as 

 crystals of green earth or Chlorite of Verona, sometimes 

 as a peculiar substance under the name of green fossil, 

 (green fossil W.) The same rock contains the green earth 

 of Verona, (chlorite baldoque, or talc zographique. ) 



The variety of Pyroxene which has been described as 

 Jeffersonite as I have mentioned, offers also an instance 

 of decomposed Pyroxene, (see Jour. Acad. Nat. Science, 

 vol. 2, part 2, p. 194.) This Pyroxene corresponded with 

 what is called Limbilite. We find it of an ochre yel- 

 low colour of an earthy appearance, and sufficiently soft 

 to be scratched with the finger nail, having nevertheless, 

 preserved its lamillar structure. By dividing mechani- 

 cally a crystal in order to detect the direction of the lu- 

 mina, I cut with a common knife upwards of 1-8 of an 

 rnch deep without injuring the edge of the knife, it then 

 became harder and harder, and at last hard enough lo 

 scratch glass; in all these stages the structure was preser- 

 ved. Those varieties which are only slightly decompo- 



