Cerussite, lead carbonate,
Formula PbCO3.

Crystal system: Orthorhombic (crystal form usually tabular, hexagonal bipyramids or acicular).
Hardness: 3 to 3.5
Density: 6.4 to 6.6 gms/cm3
Colour: Colourless, white, yellow, grey, brown or black.
Streak: White.

Cerussite is a common supergene mineral formed in the oxydation zones of lead deposits. It is produced by reaction between carbon dioxide and galena (lead sulphide) with which it commonly occurs. Really fine lustrous crystalline specimens were found at Tsumeb in Namibia.

The specimen shown in the picture came from Tsumeb, Namibia, South West Africa.

Cerussite from Tsumeb, Namibia, South West Africa