i y6 Count de Bournon’s Description of 
Second Species. Arseniate of Copper in hexaedral lamina, 
with inclined sides. 
This species is commonly found in very fine hexaedral lami- 
nae, The six narrow sides of these laminae have an inclined posi- 
tion, alternately in a contrary direction, on the two broad planes, 
in such a manner that each of the planes is encompassed by three 
sides, which are inclined upon it. (Fig. 3.) As far as the small 
size, and more particularly the thinness of these crystals, has 
enabled me to judge, two of these three inclined sides, form 
an angle of about 135 0 with the broad planes on which they 
incline ; and the third, one of 115 0 . 
The two broad planes are smooth, and have a very brilliant 
lustre. The six narrow sides are rendered very dull, by the great 
number of striae with which they are covered ; most of which are 
very prominent, and all are parallel to the edges of the broad 
planes. In consequence of this, these crystals may be divided, 
parallel to the planes, almost as easily as crystals of mica. 
This structure prevents the crystal from being considered as 
a modification of the octaedron : that which would be produced 
by an increase of the inclined sides, would only be a secondary 
crystal ; and none of the specimens I have seen, give mereason 
to suppose the existence of such a variety. 
The colour of this species is a fine deep emerald green ; some- 
times, though rarely, it is found of a lighter colour. The lustre 
of its broad planes, which are the only parts of the crystal that 
forcibly strike the eye, give it pretty much the appearance of those 
coloured metal plates which are known by the name of foil. 
This species is still less heavy than the preceding ; its spe- 
cific gravity being only 2,548. 
