CERUSSITE WITH LINARITE & POSNJAKITE
ABOUT THE SPECIMEN
Among the list of unique mineral combinations that Tsumeb produced, this combination of cerussite and linarite is particularly elusive, virtually impossible to find on the open market. Not only is it rare, it also has a captivating and highly aesthetic, almost "icy" appearance. The deep blue linarite is grown closely together with blue-green posnjakite, an uncommon copper sulfate. I've seen other samples of this material, this one however is in a league of its own. The linarite and posnjakite each formed in different stages, both as inclusions within and as a coating atop the cerussite crystals, and some of the linarite is clearly formed in small crystals. The cerussite is lustrous, gemmy, and well-formed, with numerous reticulated "snowflake" twins covering both sides. There are some areas of other copper mineralization which looks to be brochantite. These pieces are generally said to have come out of the first oxidized zone in the 1920's, and I feel comfortable dating it back to that period of mining. It's rare to find a "one of one" specimen from a mine that produced so much material over almost a century, yet I believe this one deserves such a distinction.
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Cerussite specimens with internal linarite and posnjakite represent one of Tsumeb's more unusual mineral associations, documenting the complex paragenetic sequences within the first oxidation zone. These pieces typically feature tabular cerussite crystals with adamantine luster and varying degrees of translucence, hosting internal zones of deep blue linarite alongside greenish-blue posnjakite inclusions. The assemblage forms through a specific Type II paragenetic sequence first described by Keller in 1977, where primary sulfides weather to brochantite and posnjakite, followed by linarite formation under acidic conditions. What makes these specimens mineralogically significant is that the inclusions preserve a snapshot of this progression - the copper sulfate minerals formed first and were then trapped during cerussite crystallization from lead-bearing solutions. Most commonly, linarite occurs as partial coatings or near-surface inclusions in cerussite, but pieces with both copper minerals distinctly visible within a single crystal are considerably rarer. The color contrast between the two copper species - linarite's deeper blue against posnjakite's lighter blue-green - makes these combinations visually diagnostic and particularly valued by systematic collectors focused on Tsumeb's oxidation zone mineralogy. While cerussite itself is abundant at Tsumeb, specimens preserving this specific three-mineral association in clearly observable form are scarce enough that they've become recognized as a distinctive Tsumeb type.