Transformation of Chlorite to Smectite Through Regularly Interstratified Intermediates

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Abstract
Trioctahedral, iron‐rich chlorite separated from east Texas lignite overburden shales by high gradient magnetic separation was characterized by XRD and by IR spectroscopy. The chlorite was then subjected to chemical oxidation by digestion (ca. 100°C) in a saturated bromine solution to simulate weathering. X‐ray diffraction indicated that the chlorite was transformed to smectite through regularly interstratified chloritevermiculite and chlorite‐smectite intermediates. The smectite ultimately dissolved. All of the chlorite reacted in 2 weeks. Electron micrographs of partially weathered particles of chlorite showed thin plates folded at the edges and unreacted cores in the center. Iron released during the reaction tended to precipitate along particle edges. It is postulated that the thin, folded edges and the cores were smectite and chlorite, respectively. Formation of the iron‐rich chlorite in the lignite overburden shales probably resulted from interactions between aluminous smectite and solutions rich in ferrous Fe. Exposure of the overburden shales to oxidizing conditions may result in the transformation of chlorite to smectite with precipitation of released Fe.

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