Acta Musei Moraviae

Revision of historical samples of miesite in the mineralogical collection of the Moravian Museum in Brno: a contribution to the history of pyromorphite research

Revision of historical samples of miesite in the collection of the Mineralogy and Petrography Department of Moravian Museum, Brno, Czech Republic, has proven the classification of this “mineral” as calcium-rich pyromorphite, as already known in the 19th century. However, a new microscopic and especially chemical study leads to the conclusion that in typical concentrically zonal aggregates of miesite, the Ca content in the M-position reaches pyromorphite-phosphohedyphan boundary (slightly exceeding 1 apfu Ca in Ca-rich zones – the darkest in BSE). In the anionic part of the formula (TO₄)₃, P dominates, while the content of As and S is below the limit of detection of electron microprobe. The predominant element at X-position is Cl; on the contrary, F and probably also (OH) do not reach significant values. A typical miesite forms only dark brown hemispherical aggregates immediately on galena surface in a galena-quartz gangue. Rarely miesite (Ca-rich pyromorphite) are coated both an amorphous Al-Si and Pb-Al-Si-S phosphate phases. In the case of some samples of miesite from the Stříbro locality, especially the light brown ones, it is in fact probably a barite.