Abstract

The presence of a lithiophorite interface between cryptomelane and florencite, kaolinite, and goethite in coatings on weathered siltstone at Lake Moondarra in northwest Queensland (Australia) is explained as the result of redistribution of ions originally adsorbed onto amorphous Mn oxides. Large cations (radius ∼ 1.3 Å) were accommodated in cryptomelane, with smaller cations and anions moving outward until the nucleation of lithiophorite stabilized the 0.7-Å-radius cations and some Al. Rare-earth elements and other cations of ∼ 1.0-Å radius were then stabilized as florencite, which formed with kaolinite and goethite in an outer thin band.

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