Troost on the Pyrowene, 61 
as in the lava. Mr. Cordier has pointed out that Py- 
roxene, in very minute grains, and felspar, formed the 
constituents of lava. Those known by the name of Ba- 
salt lava, lithoide trappeenes, or argilo-ferruginous va- 
rieties, are those in which Pyroxene is in greater pro- 
portion than the felspar. Currents of lava of this nature, 
offer merely scorise, and these are nothing more than 
a kind of half vitrified substance, not being changeable 
into glass; or in other words, does not form Obsidian, 
owing to the infusibility of the Pyroxene. It is from 
the surface and even from the interior of these scoria, that 
the most perfect crystals are taken, which are found where 
these substances are decomposed ; another time they are 
thrown up, sometimes in immense quantities, during cer- 
tain eruptions of the volcano, of which Etna and Vesuvi- 
us have given many instances. 
Etna, Vesuvius, TenerifFe, the Isle of Bourbon, Gua- 
deloupe, &c. furnish fine isolated crystals of Pyroxene ; 
they are found in many parts of Cantal, Velay, at Puy 
de Corent, de la Rode, de la Vache and Mural, in Au- 
vergne, in Provence, in Saxony, Bohemia, Russia, Plun- 
gary, and at Cap de Gate in Spain. |||^ 
The ferruginous volcanic sands of Pouzzole near Na- 
ples, which are melted there, contain large quantities of 
very minute granular Pyroxene, owing to the disinte- 
grations of the lavas, which the sea washes to the shore. 
The sands and ashes which the volcanoes throw up are. 
loaded with this substance. 
2. Green P. (Rirescite.) This variety has commonly 
a yellowish green or brownish colour, and is half trans- 
lucent, or of a dark dull green. It occurs mostly in the 
unaltered rocks which are thrown up by the volcanos, 
er in the volcanic sands. In the ancient lavas it is found 
Vox. I. 9 
