Hydrocerussite

carbonate

cerussite

Formula: Pb3(CO3)2(OH)2
Anhydrous carbonate containing hydroxyl
Specific gravity: 6.8
Hardness: 3½
Streak: White
Colour: White or grey; colourless in transmitted light
Solubility: Soluble in acids with effervescence
Environments:

Metamorphic environments
Hydrothermal environments

For carbonate concentration slightly lower than atmospheric, cerussite and hydrocerussite can co-exist in alkaline environments, with leadhillite in more acid environments, and anglesite in yet more acid environments. For lower carbonate concentrations hydrocerussite completely replaces cerussite. In these conditions anglesite and hydrocerussite cannot co-exist (JRS 18.11).

At the type locality cerussite occurs in a metamorphosed Mn-Fe deposit. It is usually a secondary mineral developed in the oxidised portions of lead deposits, but it can also be primary (R&M 93.2.150).

In Tsumeb, Namibia, hydrocerussite may be of primary origin, but usually it is a secondary mineral, formed by the alteration of cerussite. This requires highly alkaline conditions with a pH of 10 to 13, and a constant and stable concentration of carbonate ions in solution. These conditions are most likely only at depth, and indeed a deep pocket has been found which yielded twinned cerussite partially or wholly replaced by hydrocerussite, associated with litharge, massicot, minium and scotlandite, all occurring as microcrystals on the hydrocerussite. Other associated minerals include dundasite, galena, smithsonite, mottramite, dioptase, plancheite, cobaltoan dolomite, tennantite and wulfenite. Hydrocerussite from Tsumeb rarely forms as pseudomorphs after anglesite.
Tsumeb hydrocerussite has been found from three different mineral assemblages. Firstly scaly aggregates associated with azurite, malachite, mimetite and calcite (the hydrocerussite occurs only on the azurite). Secondly intergrown with or overgrown on cerussite, associated with arsentsumebite, azurite, malachite, mimetite and phosgenite. Lastly as pseudomorphs of hydrocerussite after cerussite; some of these crystals still contain unaltered cores, and these are associated with mimetite, duftite and dolomite (R&M 93.2.150-151).

At Långban, Sweden, hydrocerussite is most commonly found as an alteration product of native lead, associated with litharge, hausmannite or clinopyroxene skarn (R&M 93.2.155.).

At the Higher Pitts Mine, Mendip Hills, England, UK, hydrocerussite is fairly common as massive nodules, and also forms as an alteration product around nodules of mendipite (R&M 93.2.153-154).

At the Mammoth-Saint Anthony Mine, Tiger, Pinal county, Arizona, USA, hydrocerrusite is associated with diaboleite, caledonite, paralaurionite and cerussite (R&M 93.2.155).

Alteration

Litharge, CO2 and H2O to hydrocerussite
3PbO + 2CO2 + H2O → Pb3(CO3)2(OH)2
Synthetic hydrocerussite can be easily obtained, as a white powder, by the action of carbon dioxide and water on litharge at pH 4 to 5 (R&M 93.2.150).

The mendipite-hydrocerussite equilibrium reaction is
mendipite + CO2 + water ⇌ hydrocerussite + H+ + Cl-
Pb3O2Cl2 + 2CO2 + 2H2O ⇌ Pb3(CO3)2(OH)2 + 2H+ + 2Cl-
(JRS 15.27)
An ample supply of CO2 favours the forward reaction.

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