Anthropogenic humboldtine from Cornwall, England

Abstract

A pyrite specimen from Wheal Jane, Cornwall on which a crust of the rare iron oxalate mineral humboldtine had crystallised was recently identified in the Manchester Museum mineral collection. Careful examination indicates that the humboldtine is of anthropogenic origin and so it is not a natural mineral. It seems likely that it was produced during an attempt to clean the specimen in oxalic acid. Cleaning processes can modify mineral assemblages and it is worthwhile making a careful study of specimens to determine whether all of the minerals present are natural. Unusual mineralogical combinations such as the organic oxalate mineral humboldtine in a high temperature hydrothermal mineral vein should be treated with caution. There is no credible geological source for the oxalate anion in this system. The absence of such a source casts doubt on the only other British report of humboldtine from Pendarves Mine, Cornwall.