The analyses are reported of six Australian coals for mineral type and content, B, Se speciation (by selective leaching) and S speciation (by selective leaching and XANES) together with XANES data for Se in one coal (from a marine sequence). The results of these analyses and of thermodynamic calculations of thiophenes and Se analogues are used to suggest that selenoprotein structures in coal's precursors (bacteria and algae and possibly higher plants) make Se bonding in coal unique from that of the other trace elements. Crown Copyright (C) 2007 Published by Elsevier B.V. All rights reserved.