Sulphuret of Iron. Pyrites

These crystals were commuicated by the Rev. H. Davies, from Parys Mine, Anglesea, where there is great abundance in some places, heaped together like grains of sand, so small that their lustre is lost in their minuteness, much less can the cubic form be seen without a magnifying glass. The rocks of Amorphous Feldspar,a nd those passing to rgular slate, contain them of different sizes. The upper figure is from a specimen of gangue of which is between common limestone and slate, and contains no small quantity of the crystals. The gangue is in the softer parts stained a little green, perhaps from some oxide of copper. The lower figure is a piece of undulated (otherwise common blue) slate, which is a durable sort if free from pyrites, as the common air decomposes the pyrites, decays the iron, and the slate becomes rotten. This will be further explained when we are treating the best slate of Wales, Westmoreland, Yorkshire, Cornwall, &c.