Cerussite

Cerussite


Composition: PbCO3
Crystal System : Orthorhombic
Colours: Colourless, white, yellow, brown, grey, black, red
Lustre : Adamantine, Vitreous, Resinous, Pearly, Dull, Earthy
Hardness (H) : 3.0-3.5
Specific Gravity (S.G) : 6.53-6.57
References: Gebhard (1999)

Distribution

Abundant. Occurs in all three oxidation zones.

Occurrence

  • Supergene
  • 1st Oxidation Zone
  • 2nd Oxidation Zone
  • 3rd Oxidation Zone

Notable Finds

In the first oxidation zone cerussite was found to a depth of c.400m but not beyond (Gebhard, 1999), with the best crystals found between 150m and 250m below surface (Von Bezing, 2014). In the 1970s, fine cerussite crystals were found in abundance in the second oxidation zone and, notably, very fine reticulated groups were recovered from the manto ore bodies (Clive King, private communication to M. Southwood, 2013). In the third oxidation zone, the so-called "Lead Pocket" was found on 43 Level and was noted, inter alia, for hydrocerussite replacing cerussite crystals to varying degrees. Fine examples of red cerussite (coloured by inclusions of cuprite) were also recovered (separately) from these deepest workings (Gebhard, op. cit.).

Paragenetic and General Notes

Cerussite is by far the most abundant secondary lead mineral at Tsumeb (Keller, 1977). Crystals to 600 mm are known. Most are twinned on (110). Sixlings and trillings are very common, and the reticulated "honeycomb" or "snowflake" habits of cerussite are the result of repeated twinning. Heart-shaped twins on (130) are very much rarer (Von Bezing et al., 2014). Cerussite is a common mineral and assemblages rich in cerussite are numerous.

Cerussite is an important component of Keller's (1977) "Type I" parageneses (i.e. mineral sequences forming at higher pH ranges). Keller notes the following sequences:

(1) goethite >> duftite(i) >> cerussite >> duftite(ii) >> dolomite.

(2) dundasite >> smithsonite(i) >> cerussite >> smithsonite(ii).

(3) cerussite >> duftite >> malachite >> mimetite

(4) duftite(i) >> malachite >> cerussite >> duftite(ii).

(5) duftite >> dundasite >> cerussite >> azurite >> malachite (ps. azurite).

(6) primary sulphides >> wulfenite >> alamosite >> kegelite >> leadhillite >> cerussite.

Cerussite is reported to form pseudomorphs after the following minerals: anglesite (common); galena (rare); leadhillite (rare); mimetite (rare); phosgenite (rare).

The following minerals are reported to form pseudomorphs after cerussite:  arsentsumebite (rare); calcite (rare); dolomite (rare); hydrocerussite (common); mimetite (rare); smithsonite (rare); willemite (rare).