“…Metallic-Pb nanospheres have, to date, only been characterised using transmission electron microscopy (TEM) and are estimated to contain in excess of 139,000 Pb atoms within a ~20 nm diameter nanosphere (Kusiak et al , 2017). Investigations of Pb in zircon at the atomic scale using atom probe tomography (Valley et al , 2014, 2015; Piazolo et al , 2016; Peterman et al ., 2019; Arcuri et al , 2020), describes ‘atomic Pb clusters’, however these are relatively small in terms of Pb concentration, typically comprising no more than a few thousand Pb atoms, and are thus distinct from metallic-Pb nanospheres.…”