Micromorphological investigation of pedogenic barite in Mormon Mesa petrocalcic horizons, Nevada USA: implication for genesis.

摘要

Barite crystals are identified in stage VI petrocalcic horizons at Mormon Mesa, Nevada. Their presence is significant because barite is not typically associated with arid soil processes. Barite is identified through backscatter SEM/EDS as bright white crystals with EDS peaks of high Ba, S, and O. Barite crystals are euhedral, tabular to acicular crystals ranging in size from 1 to 50 micro m in length and 1-20 micro m in diameter, and as small (2-4 micro m) tabular-ovoid crystals. Forty-one percent of the barite in SEM images is associated with fibers of palygorskite and/or sepiolite. Barite crystals are also associated with linear voids, circular pores, and within micropores between fibers of silicate clays. The formation of barite at Mormon Mesa is attributed to: (i) The dissolution of Ba and SO₄ ions from detrital minerals and dust that are flushed into the soil profile and precipitate as barite; and/or (ii) Biomineralization of barite in micro-environments suitable for bacteria or other organisms within the petrocalcic horizon.