Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/39

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of the red oxyd of Copper and arseniated Iron.

place this mineral also was found in the Gossan before described, occasionally 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 the first discovery of the red oxyd took place. The cubic arseniate of iron 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 angle 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 modifications 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, where the same modifications occur, but in which each of those angles that are not replaced by the two modifications as in fig. 3.