52 Troost on the Pyroosene. 
base forms, with the edge of the prism, corresponding witk 
the two obtuse angles, angles of 106° 6' and 73° 54'. In the 
primitive nucleus of the Amphibole, which is also an obtuse 
rhomboidal prism, the inclinations of the planes of the prism 
are to each other 124° 34' and 55° 26', a difference so great ^ 
as to be easily recognized. In the nucleus of the Pyroxene, 
the smaller diagonal of the base is to the length of one of 
the edges of the prism, nearly as 18 to 5; in the Amphibole, 
on the contrary, it is nearly as 4 to 1. The nucleus of the 
Pyroxene is divisible, in the direction of the two diagonals 
of the base, into four oblique triangular prisms. 
The varieties of Pyroxene, which have been considered 
as so many different species, have given to Hauy the same 
primitive nucleus.* 
Pyroxene is generally black or green, or offers interme- 
diate shades between these two colours; it is also whitish 
green or greenish white, sometimes grey, rarely white; its 
longitudinal fracture is lamellar, and this fracture is more 
or- less apparent, according to the varieties; its transverse 
fracture is granular, uneven, or conchoidal. It is seldom 
transparent, mostly translucent oh the edges, or opaque. 
When transparent, it is endowed with the double refracting 
power. It is hard enough to scratch glass. Forms a dark 
green, or greyish green powder. In general, its sp. gr. varies- 
from 3.223 to 3.373. It melts before the blow pipe with 
difficulty, into a brownish or whitish glass. 
The varieties of Pyroxene have given, by. analysis, near- 
ly one half silex; lime and magnesia, in a quantity equal 
* This departed sag-e, in whom I deplore the loss of a true friend, has 
made investigations of these different varieties the subject of many me- 
moirs which were published in the Annates and Memoirs of the Museum 
of Natural History; where those who wish to study the manner in which 
the laws of crystallization are explained, and the results that are to be 
deduced, may satisfy themselves. 
i 
