64 
Troost on the Pyroxene. 
sublimed or washed away. We may observe in nearly 
all the craters, and particularly in the solfutara, decom- 
posed lavas which contain crystals of Pyroxene perfect- 
ly well formed, also in a state of decomposition. 
The calcinations which the lavas undergo continually 
around the burning craters, does not act so effectually 
upon the crystals of Pyroxene. These are often in a 
perfect and unaltered state at the same time that the la- 
vas are crumbling to dust. Dolomieu has collected in the 
crater of Monte Roso, a yellow resinoid Obsidian, con- 
taining Pyroxene covered with a thin white pellicle ; he 
collected in the same crater, red scoriae containing the 
same crystals. This scoriae, which is very brittle, is form- 
ed by the natural calcinations of the glassy lava ; this is 
easily ascertained by the blow-pipe, which converts this 
lava into the same scoriae. Dolomieu saw specimens 
which presented the two varieties. It is besides known 
that unaltered crystals of Pyroxene occur in vitrified la- 
va ; it is only by a long continued action of heat that they 
crack and fall at last to dust. 
Even the other atmospheric agents, only after a very 
long exposure, have a slight action on Pyroxene ; and 
it is to this circumstance that we ascribe the perfect con- 
servations of the currents of ancient lava which are yet 
in existence, and have all the appearance of having been 
recently formed. The Basalt and other volcanic produc- 
tions having Pyroxene as a base, are in the same case. 
Pyroxene offers, nevertheless, two different states of 
decomposition ; in the one, it becomes of a rusty or earthy 
j^ellow. It preserves partly its lamillar structure, and is 
friable. Some naturalists have made of it a species under 
the name of Limbilite. The lava of Teneriffe, Bourbon, 
Brisgau, offer instances of this kind ; the decomposed 
Pyroxene occurs here with perfect unaltered crystals, 
