Tin weathering experiment set by nature for 300 years: natural crystals ofthe anthropogenic mineral hydroromarchite from Creussen, Bavaria, Germany

Hydroromarchite is a mineral that so far has been found only in afew locations in the world and recognized as a common product of submarinecorrosion of pewter artefacts. Here we report a new locality for this raremineral found at the Saint James Church archaeological site in Creussen,Germany. There it appeared to be a product of weathering of a tin artefact(a tin button) buried in soil of the churchyard for about 300 years. Themineral, found in paragenesis with romarchite and cassiterite, wasidentified using single-crystal X-ray diffraction.