PHOSGENITE  , a rare.

mineral consisting of lead chlorocarbonate, (PbCI)2CO3 . The tetragonal (holosymmetric) crystals are prismatic or tabular in habit, and are bounded by smooth, bright faces: they are usually colourless and transparent, and have a brilliant adamantine lustre . Sometimes the crystals have a curious helical twist about the tetrad or principal axis . The hardness is 3 and the specific gravity 6.3 . The mineral is rather sectile, and consequently-was early known as " corneous lead " (Ger . Hornblei) . The fanciful name phosgenite was given by A . Breithaupt in 1820, from phosgene, the old name of carbon oxychloride, because the mineral contains the elements carbon, oxygen and chlorine . At Cromford, near Matlock, it was long ago found in an old lead mine, being associated with afiglesite and matlockite (Pb2OC12) in cavities in decomposed galena: hence its common name cronfortite . Fine crystals are also found in galena at Monteponi near Iglesias in Sardinia, but the largest are those recently found near Dundas in Tasmania . Crystals of phosgenite, and also of the corresponding bromine compound [PbBr]2CO3, have been prepared artificially . (L .

J .