Irony Arsenic

This substance much resembles the whitish Iron Pyrites or arsenical Sulphuret of Iron, and seems to have been partly confounded with it by Kirwan; who observes, that “the Marcasite found near Dublin, called Irish Diamonds, is of this species.” This latter is however to be most readily distinguished by the crystals being right-angled^*, whereas the present is an acutely rhomboidal prism. It is perhaps not unnatural for Irish Pyrites to have a little arsenic, but not in sufficient quantity to characterize a species. The colour is different in the interior; one being a grayish white, the other yellowish.

The specimen figured came from Cornwall, and is remarkable for having somewhat acicular crystals collected in divaricating bunches, which pervade Blende, Copper Pyrites, and Quartz. Before the blowpipe it melts easily, gives out copious white fumes strongly scented with Garlic, and highly noxious to the lungs: what remains is a small gray globule of magnetic Iron.

The right hand figure shows the primitive rhomboidal termination of an elongated crystal, with a decrement upon the obtuse solid angle. The face produced by this decrement gives for its incidence upon the rhomboidal face 149° or thereabouts: this modification seems to be new, as Haüy has not mentioned it.

The left hand figure represents another view of the primitive, with a decrement on the acute angle, which agrees with letter s of Haüy’s fig. 137.