Phosgenite

Phosgenite is a rare mineral consisting of lead chlorocarbonate, (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).[5]

Phosgenite
Crystal of phosgenite from the Monteponi Mine, Iglesias, Sardinia, Italy (size: 3.0 x 3.0 x 2.5 cm)
General
CategoryCarbonate minerals
Formula
(repeating unit)		(PbCl)2CO3
Strunz classification5.BE.20
Crystal systemTetragonal
Crystal classDitetragonal dipyramidal (4/mmm)
H-M symbol: (4/m 2/m 2/m)
Space groupP4/mbm
Unit cella = 8.16 Å, c = 8.883(6) Å; Z = 4
Identification
ColorPale yellow to yellowish brown, pale brown, smoky brown, smoky violet; colorless, pale rose, gray, yellowish gray, pale green
Crystal habitShort prismatic crystals, granular, massive
CleavageDistinct on {001} and {110}, indistinct on {100}
FractureConchoidal
TenacitySectile, flexible perpendicular to {001}
Mohs scale hardness2 – 3
LusterAdamantine
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity6.12 – 6.15
Optical propertiesUniaxial (+); anomalously biaxial if strained
Refractive indexnω = 2.118 nε = 2.145
Birefringenceδ = 0.027
PleochroismWeakly pleochroic with O - reddish and E - greenish in thick sections.
Ultraviolet fluorescenceFluoresces yellow under LW and SW UV
SolubilitySoluble in dilute nitric acid with effervescence, decomposes slowly in cold water
References[1][2][3][4]

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, from phosgene, carbon oxychloride, because the mineral contains the elements carbon, oxygen and chlorine.[5]

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.[6] Crystals are also found in galena at Monteponi near Iglesias in Sardinia, and near Dundas in Tasmania.[5] 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 Rosalia, Baja California. 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.[2]

Crystals of phosgenite, and also of the corresponding bromine compound PbBr2CO3, have been prepared artificially.[5]

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References
  1. Mineralienatlas
  2. Handbook of Mineralogy
  3. Mindat.org
  4. Webmineral data
  5.  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. 21 (11th ed.). Cambridge University Press. p. 474.
  6. "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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