a radiated sulphate of barytes, found in roundish masses, composed of radiating fibres. When calcined, pulverized, converted into a paste with mucilage, and then dried in pieces about a quarter of an inch thick, it 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. It was first discovered at Monte Paterno near Bologna, whence it derives its name.