Phosgenite

(repeating unit)(PbCl)2CO3IMA symbolPho[1]Strunz classification5.BE.20Crystal systemTetragonalCrystal classDitetragonal dipyramidal (4/mmm)
H-M symbol: (4/m 2/m 2/m)Space groupP4/mbmUnit cella = 8.16 Å, c = 8.883(6) Å; Z = 4IdentificationColorPale yellow to yellowish brown, pale brown, smoky brown, smoky violet, colorless, pale rose, gray, yellowish gray, pale greenCrystal habitShort prismatic crystals, granular, massiveCleavageDistinct on {001} and {110}, indistinct on {100}FractureConchoidalTenacitySectile, flexible perpendicular to {001}Mohs scale hardness2–3LusterAdamantineStreakWhiteDiaphaneityTransparent to translucentSpecific gravity6.12 – 6.15Optical propertiesUniaxial (+); anomalously biaxial if strainedRefractive indexnω = 2.118 nε = 2.145Birefringenceδ = 0.027PleochroismWeakly pleochroic with O – reddish and E – greenish in thick sections.Ultraviolet fluorescenceFluoresces yellow under LW and SW UVSolubilitySoluble in dilute nitric acid with effervescence, decomposes slowly in cold waterReferences[2][3][4][5]

Phosgenite is a rare mineral consisting of lead carbonate chloride, (PbCl)2CO3. The tetragonal crystals are prismatic or tabular in habit: 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, (German Hornblei).[6]

Name and occurrence

An example of the mineral Phosgenite on display at the Royal Ontario Museum

The name phosgenite was given by August Breithaupt in 1820, after phosgene, carbon oxychloride, because the mineral contains the elements carbon, oxygen, and chlorine.[6]

It was found associated with anglesite and matlockite in cavities within altered galena in a lead mine at Cromford, near Matlock: hence its common name cromfordite.[7] Crystals are also found in galena at Monteponi near Iglesias in Sardinia, and near Dundas in Tasmania.[6] It has also been reported from Laurium, Greece; Tarnowitz, Poland; the Altai district, Siberia; the Touissit mine, near Oujda, Morocco; Sidi Amor ben Salem, Tunisia; Tsumeb, Namibia; Broken Hill, New South Wales; and Boleo, near Santa Rosalía, Baja California Sur. In the US it has been reported from the Terrible mine, Custer County, Colorado; the Stevenson-Bennett mine, Organ Mountains, Doña Ana County, New Mexico; and the Mammoth mine, Tiger, Pinal County, Arizona.[3]

Crystals of phosgenite, and also of the corresponding bromine compound PbBr2CO3, have been prepared artificially.[6]

See also

References

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Mineralienatlas
  3. ^ a b Handbook of Mineralogy
  4. ^ Mindat.org
  5. ^ Webmineral data
  6. ^ a b c d  One or more of the preceding sentences incorporates text from a publication now in the public domain: Spencer, Leonard James (1911). "Phosgenite". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 21 (11th ed.). Cambridge University Press. p. 474.
  7. ^ "Phosgenite and Matlockite in Derbyshire (Part 1). T. Bridges, M. E. Smith. Journal of the Russell Society Volume 1, No. 2, p.7–14, 1983 Retrieved on 2011-01-11
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