Nontronite NAu-1 was exposed to moderate temperature and pressure conditions (250 and 300°C at 100 MPa pressure) in KCl brine to simulate burial diagenetic systems over accelerated time periods appropriate for laboratory experiments. Powder X-ray diffraction and transmission electron microscopy analysis of the coexisting mixed-layer and discrete 10 Å clay reaction products, and inductively coupled plasma-mass spectrometry analysis of the remaining fluids, indicated that the clay retained octahedral Fe and was identified as Fe-celadonite. The release of Fe from smectite during burial diagenesis has been hypothesized as a mechanism for magnetite authigenesis. High Al activity relative to Fe may be critical to the formation of an aluminous illite and any associated authigenic magnetite.

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