SOME SEA GLASS PEBBLES FROM SÃO MIGUEL AZORES, PORTUGAL: PHYSICAL FEATURES, CHEMISTRY AND POTENTIAL RAW MATERIALS

Three Sea Glass pebbles collected on the shoreline of the island of São Miguel Azores, in Portugal, called white, blue and black, were analyzed by mesoscopic means, and by XRD, XRF (handheld), and SEM-EDS. They are rounded, matte, and translucent, with a hardness of around 6 and low density. They are all amorphous to XRD. All three have the same proportion in Si (SiO2) and Al, while they differ in most of the other chemical components. White and blue are sodium-potassium-barium, and black are sodium-calcium. Blue has Co as its pigment, while black has Fe/Mn oxyhydroxides. It is likely that quartz sand, quartz containing Al and Ti, was added at least in part as plant ash (Na, K, Mg, S, Cl). However, Ba may have had calcined barite as its raw material, which appears sporadically in microaggregates. Therefore, the Azores SG could be classified as possible genuine sea glass.