The interaction of various solvents with some clays that are commonly found in coal has been examined. The mixed solvent N-methyl-2-pyrrolidinone/carbon disulfide can extract cations from various clays and apparently form complexes with them that strongly absorb light in the visible region. The individual solvents cannot form such complexes when placed in contact with the same clays. The ability to form such complexes with cations may be a key factor in the enhanced extraction yields that are obtained from certain coals using this mixed solvent system.