of the red oxyd of Copper and arseniated Iro7i. 27 



place thl9 mineral also was found in the Gossan before described, oc- 

 casionally intermingled with arseniate of copper. The latter occurred, 

 besides, in great abundance in the same lode in Huel Unity; indeed, 

 I believe it is to that part of the united lodes which passes through 

 this mine, that mineralogists are chiefly indebted for the fine varieties 

 of the arseniate of copper. 



That beautiful mineral, the cubic arseniate of iron, was also found 

 at and near the junction of the Great Gossan and Muttrell Lodes ; 

 but occurred in greatest quantity in the latter, thirty fathoms west of 

 the junction, about the adit level ; being forty-six fathoms higher, 

 though perhaps not immediately above the part in which tliS ^%i 

 discovery of the red oxyd took place. The cubic arseniate of ijfon 

 was also found in the Gossan before described. 



Since the publication in the Philosophical Transactions of the 

 .paper by the Count de Bournon, containing a description of this 

 mineral, I have obtained some varieties in the form of its crystal, 

 not described in that paper. In addition to the perfect cube (fig. 1.) 

 and that modification of it, by which four of its solid angles are 

 replaced by an equal number of equilateral triangular planes (fig. 2.) 

 -as described by the Count de Bournon, I possess some in which 

 each angk so modified has received an additional modification, by 

 three triangular planes placed on the edges, and inclining to the axis 

 of the crystal. This variety however rarely occurs in the perfection 

 in which it is represented by fig. 3. for, generally, the two modifi- 

 cations are so blended together, as to give a roundness to the whole 

 as in -fig. 4. I possess also others in which the edges of the cube 

 are replaced by planes (fig. 5.) ; others in which the modifications 

 described in figs. 3 and 5 are combined, as in fig. 6 : others again, 

 AVhere the same modifications occur, but in which each of those 

 angles that are not replaced by the two modifications as in fig. 3. 



d2 



