Precipitate formation sepiolite

Sepiolite and palygorskite have a rather special composition and seem to be related to specific mineral parageneses. They appear to be stably associated with montmorillonite, corrensite, serpentine, chert, sulfates, carbonates and various salts. They are found in deposits typified by processes of chemical precipitation or solution-solid equilibria (Millot, 1964) and are therefore rarely associated in sediments with large quantities of detrital minerals. Their chemical environment of formation is in all evidence impoverished in alumina and divalent iron. Their frequent association with evaporites, carbonates and cherts indicate that they came from solutions with high chlorinity. 

The experimental values for the free energies of formation of kaolinite and sepiolite are given in Tbble II. The value of -907.7 +1.33 kcal/mol recommended for kaolinite, is the mean of three recomputed free energies of formation weighed equally in the computation, and was obtained from calorimetry, dissolution, and precipitation data. Several values in the -905 to -906.0 kcal/mol range probably reflect the more soluble nature of small particles typically present in bulk samples. 

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