Phosgenite

minerals

cotunnite

leadhillite

cerussite

Formula: Pb2(CO3)Cl2 anhydrous carbonate containing halogen
Specific gravity:
Hardness: 2 to 3
Streak: White
Colour: Colourless, white, yellow, brown, greenish or pink; colourless in transmitted light
Solubility: Moderately soluble in nitric acid with effervescence. Decomposed slowly in cold water, which extracts lead chloride
Environments:

Hydrothermal environments

Phosgenite is a secondary mineral found in the weathered zone of lead ore deposits. It readily alters to, and is replaced by, cerussite

Stability

The Activity-pH diagram below was calculated for some lead minerals. Boundaries are calculated for constant activity (roughly equivalent to concentration) of (SO4)2- and constant partial pressure (also roughly equivalent to concentration) of CO2, over a range of values of pH and of Cl1- activity. In this case the concentration of CO2 is appreciably more than the atmospheric value.
Phosgenite is stable in a range of pH from somewhat acid to somewaht alkaline, with a fairly high concentration of Cl- ions (JRS 15.18-23).

stability Pb.jpg

The lead mineral formulae are:
cotunnite PbCl2
phosgenite Pb2(CO3)Cl2
cerussite Pb(CO3)
anglesite Pb(SO4)















The Activity-pH diagram below is similar but in this case the concentration of CO2 is not so much above the atmospheric value.
Paralaurionite and phosgenite can co-exist at this CO2 concentration. At higher concentrations phosgenite is the stable mineral, and at lower concentrations paralaurionite is the stable mineral (JRS 15.18-23).

stability Pb 2.jpg

The lead mineral formulae are:
cotunnite PbCl2
phosgenite Pb2(CO3)Cl2
paralaurionite PbCl(OH)
cerussite Pb(CO3)
anglesite Pb(SO4)
leadhillite Pb4(CO3)2(OH)2











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