phosgenite

{{Infobox mineral | name = Phosgenite | boxwidth = | boxbgcolor =#C4B353 | image = Phosgenite-34631.jpg | imagesize = | alt = | caption = Crystal of phosgenite from the Monteponi Mine, Iglesias, Sardinia, Italy (size: 3.0 x 3.0 x 2.5 cm) | category = Carbonate minerals | formula = (PbCl)2CO3 | IMAsymbol = Pho | molweight = | strunz = 5.BE.20 | dana = | system = Tetragonal | class = Ditetragonal dipyramidal (4/mmm)H-M symbol: (4/m 2/m 2/m) | symmetry = P4/mbm | unit cell = a = 8.16 Å, c = 8.883(6) Å; Z = 4 | color = Pale yellow to yellowish brown, pale brown, smoky brown, smoky violet, colorless, pale rose, gray, yellowish gray, pale green | colour = | habit = Short prismatic crystals, granular, massive | twinning = | cleavage = Distinct on {001} and {110}, indistinct on {100} | fracture = Conchoidal | tenacity = Sectile, flexible perpendicular to {001} | mohs = 2–3 | luster = Adamantine | streak = White | diaphaneity = Transparent to translucent | gravity = 6.12 – 6.15 | density = | polish = | opticalprop = Uniaxial (+); anomalously biaxial if strained | refractive = nω = 2.118 nε = 2.145 | birefringence = δ = 0.027 | pleochroism = Weakly pleochroic with O – reddish and E – greenish in thick sections. | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = Fluoresces yellow under LW and SW UV | absorption = | melt = | fusibility = | diagnostic = | solubility = Soluble in dilute nitric acid with effervescence, decomposes slowly in cold water | impurities = | alteration = | other = | references = }}

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 ().