At Monte Paterno, about four miles from Bologna, a radiating columnar variety of barytes is found imbedded in marl, which, when heated to ignition, finely powdered, converted into a paste, and then dried in pieces about a quarter of an inch thick, affords a pyrophorus, which, after a few minutes' exposure to the sun's rays, gives light enough in the dark to render the figures on the dial plate of a watch visible. This, from its locality, is called Bolognian stone.