NMR of layered silicates in Argonne coals and geochemical implications

High-resolution Al-27 and Si-29 NMR were employed to characterize layered s ilicates in the suite of eight Argonne Premium coals. Analyses were perform ed on native coals directly, or fractions isolated by sink-float techniques . Mineral phases of kaolinite, quartz, and illite-montmorillinite clays cou ld readily be distinguished nonquantitatively by Si-29 NMR techniques using direct detection or cross polarization. Al-27 NMR was used to determine qu antitatively the amounts of tetrahedral and octahedral aluminum forms prese nt. The Al-27 NMR results were consistent with mineralogical analyses by XR D, showing that increases in tetrahedral content paralleled illitization of the clay minerals. A remarkably good relationship also was found between t he total amount of tetrahedral aluminum associated with the mineral matter and degree of maturation of the organic matter in the coal. The data sugges t that illitization of the clays can be used as a mineralogical thermal mat urity indicator for Type II kerogens, as demonstrated for the Argonne Premi um coals, provided that contributions from organo-chelated aluminum species and detrital mineral matter are taken into account.