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, w^th 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, 
(groen 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 la- 
mina, I cut with a common knife upwards of 1-8 of an 
inch deep without injuring the edge of the knife, it then 
became harder and harder, and at last hard enough to 
scratch glass; in all these stages the structure waspreser- 
yed. Those varieties which are only slightly dccorapo- 
