Sulphuret of Iron, decomposing

Sulphuret of Iron, or Iron Pyrites, under certain changes of atmosphere, forms Sulphate of Iron, or Green Vitriol, as figured in tab. 23, and often falls to pieces with efflorescence; to prevent which, and to preserve curious specimens, we are obliged to keep them immersed in water. The upper specimen was sufficiently protected by the dark, partly crystallized, outward coat, from decomposing in the common atmosphere of a room, in a damp neighbourhood; but soon after it was broken, the more porous parts put forth curls of lightish-green virtriol, and at the edges chiefly, sulphur. It still slowly decomposes, and has continued to do so for some months: in time perhaps it may fall to pieces, or remain a porous iron ochre, like the lower figure. These specimens were found among a micaceous limestone in a quarry near Godstone, in Surry, where they roll down from the top in great abundance.