Testing Greco-Roman medicinal minerals: the case study of solfataric alum

The medicinal properties of mineral pigments, mordants or washing powders presented in Pliny’s 35th book of Natural History and in those of other authors of the Greco-Roman world (Galen, Dioscorides, Scribonius) have been relatively little researched compared to their botanical counterparts. Over the last fifteen years there has been detailed geoarchaeological prospections and chemical/mineralogical analyses allowed to identify some of these minerals in their recorded places, essentially of origin largely on volcanic islands in the Aegean (Photos-Jones & Hall, 2011). The medicinal minerals of antiquity are now understood to consist primarily of layered silicates, sulphates and metal oxides/sulphides (Photos-Jones et al., 2015). Recent studies have been also focused on (1) processing methods by which raw materials could have been converted to finished products, i.e. the medicinals, and (2) assaying for purity (Hall and Photos-Jones 2005; 2009; Photos-Jones and Hall 2010). Moreover microbiological work on layered silicates from some volcanic islands in the Aegean (Samos) and stamped archaeological earths (terra sigillata) (Lemnos) has shown them to be antibacterial (Photos-Jones et al., 2015). The present research focuses on the second group of medicinal minerals, namely sulphur and sulphates and in particular solfataric alum efflorescences from two volcanic landscapes, in Greece and Italy, i.e. Melos (Western Cyclades) and Campi Flegrei (Naples), respectively. Both regions are known to have been exploited in antiquity and later periods. The chemistry and mineralogy of a small number of geological samples collected from each are examinated. For Melos, some samples have undergone field-based heating and processing while other samples have been used in microbiological testing. The results suggest that solfataric alum consists primarily of the minerals alunogen and K-alum with strong antibacterial (but not antifungal) properties. It is suggested that Greco-Roman medicinal minerals are likely to reflect long established geophagic practices incorporated within medical prescriptions, the antiquity of which may predate, by far, the historical periods. In addition, given that currently 'extreme' landscapes are the focus for the discovery of new drugs, an understanding of the nature and properties of the Greco-Roman medicinal minerals deriving from volcanic landscapes might be relevant to both antiquity and today. Photos-Jones E. & Hall A.J. 2010. Stypteria phorime as alunogen in solution: possible pointer to the gradual cooling of the Melos geothermal system. Hellenic J. Geosci., 45, 217-226. Photos-Jones E. & Hall A.J. 2011. Lemnian Earth and the earths of the Aegean. Glasgow, Potingair Press. Photos-Jones E., Keane C., Jones A.X., Stamatakis M., Robertson P., Hall A.J. & Leanord A. 2015. Testing Dioscorides' medicinal clays for their antibacterial properties: the case of Samian Earth. J. Archaeol. Sci., 57, 257-267.