Phosgenite

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Phosgenite is a rare mineral consisting of lead chlorocarbonate, (PbCl)₂CO₃. The tetragonal, holosymmetric, crystals are prismatic or tabular in habit, and are bounded by smooth, bright faces: they are usually colorless 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 earlier known as corneous lead. The fanciful name phosgenite was given by A. Breithaupt in 1820, from phosgene, 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 PbBr₂CO₃, have been prepared artificially.

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• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.