Home > Pseudomorphs – March 3 > MS1520 Goethite after Köttigite

Goethite after Köttigite - Sold

Goethite is an iron oxide hydroxide, named after German poet and philosopher Johann Wolfgang von Goethe (1749-1832). Johann Georg Lenz (1748-1832) first proposed the mineral name in his 1806 Tabellen über das gesammte Mineralreich. Köttigite is a zinc arsenate mineral, which often carries significant iron at Ojuela. Professor James Dana named köttigite in his 1850 System of Mineralogy. The mineral name honors German chemist Otto Köttig (1824-1892), who first analyzed the mineral.

This consists of iron oxide matrix, often called limonite, mainly consisting of goethite. A spray of bladed crystals to 2.5 cm spans a tight cavity. Interestingly, the cavity is lined with microcrystals of adamite, an indication of the local presence of zinc. The bladed crystals would have consumed zinc during formation, so the presence of adamite leads to one conclusion: the zinc was leached out during pseudomorphism and redeposited as adamite microcrystals. Consequently, the pseudomorph precursor contained zinc, and hence likely was köttigite. Imagine the fabulous köttigite specimen this was before the water table dropped, permitting its oxidation.