r go Count de Bourdon's Description of 
Species I. Simple Arseniate of Iron. 
This species crystallizes in perfect cubes; (Fig. 28. PlateXV.) 
sometimes, though rarely, they are a little flattened ; their sides 
are smooth and brilliant. 
The only modification I have observed in this form is, that 
four of the eight solid angles of the cube are replaced by an 
equal number of equilateral triangular planes, situated in such 
a manner, that every one of the sides of the cube becomes an 
elongated hexagon, having two angles of 90° each, and four 
of 135 0 . (Fig. 29.) Crystals modified in this way are very 
scarce. I have never seen but one such specimen, which is in 
the collection of Sir John St. Aubyn. The crystals of it are 
pretty large, and very well defined. 
The specific gravity of this species is 3,000. Its hardness 
is just sufficient to scratch calcareous spar. Its crystals, which 
are tolerably transparent, are of a dark green colour, with a 
brownish tinge; sometimes they are rather yellowish: and 
there exist some specimens of a brown yellow colour, like resin. 
I have never seen this species in any other state than that of 
perfect crystallization. 
Sometimes indeed a decomposition takes place, which causes 
the crystals to pass into the state of a pulverulent oxide, of a 
fine reddish yellow colour. In this case, as the bulk of the 
crystals is considerably diminished, there is perceived, upon 
breaking them, a considerable number of small cavities in their 
substance. These cavities are analogous to those which appear 
in the crystals of the spathose ores of iron, when they have 
passed into a similar state of decomposition. 
