Cerrussite

For centuries every decent Roman matron would paint her face with a cream containing White Lead in order to give the impression that she never saw the sun, since a decent Roman wife was expected to have ‘stayed at home and span wool’ as many gravestones put it. As well as its millennia of cosmetic use this lead carbonate forms amazing lattices of cyclically twinned crystals (known as reticular, or knee shaped) such as the 2 cm specimen in the photo.

It precipitates in the oxidised zone of ore deposits where carbonate rich groundwater has percolated through, transforming the initially deposited reduced sulphides (usually galena, see http://tinyurl.com/ms4vd46), making it a secondary mineral, produced from the primary by a geochemical event. The usual colour is white, though impurities can turn it grey or black. It has a very high lustre, making it sparkle and like all lead minerals is very dense.

As well as cosmetics it used to be a major constituent of white paint, though it is now banned for health reasons in most countries. Other forms include drusy masses and fibrous aggregations though the twinned crystals are favourites amongst collectors. Notable localities include the Tsumeb mine in Namibia (the source of this specimen), the Congo, Spain and Arizona.

Loz

Image credit: USA Geology

http://www.webmineral.com/data/Cerussite.shtml#.VEu2CBYjwzQhttp://www.gemdat.org/gem-934.htmlhttp://www.mindat.org/min-934.htmlhttp://www.galleries.com/Cerussitehttp://www.minerals.net/mineral/cerussite.aspx

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