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]
Phosgenite | |
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General | |
Category | Carbonate minerals |
Formula (repeating unit) | (PbCl)2CO3 |
IMA symbol | Pho[1] |
Strunz classification | 5.BE.20 |
Crystal system | Tetragonal |
Crystal class | Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) |
Space group | P4/mbm |
Unit cell | a = 8.16 Å, c = 8.883(6) Å; Z = 4 |
Identification | |
Color | Pale yellow to yellowish brown, pale brown, smoky brown, smoky violet, colorless, pale rose, gray, yellowish gray, pale green |
Crystal habit | Short prismatic crystals, granular, massive |
Cleavage | Distinct on {001} and {110}, indistinct on {100} |
Fracture | Conchoidal |
Tenacity | Sectile, flexible perpendicular to {001} |
Mohs scale hardness | 2–3 |
Luster | Adamantine |
Streak | White |
Diaphaneity | Transparent to translucent |
Specific gravity | 6.12 – 6.15 |
Optical properties | Uniaxial (+); anomalously biaxial if strained |
Refractive index | nω = 2.118 nε = 2.145 |
Birefringence | δ = 0.027 |
Pleochroism | Weakly pleochroic with O – reddish and E – greenish in thick sections. |
Ultraviolet fluorescence | Fluoresces yellow under LW and SW UV |
Solubility | Soluble in dilute nitric acid with effervescence, decomposes slowly in cold water |
References | [2][3][4][5] |
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]