Micromorphological evidence of barite neoformation in soils

Abstract

The occurrence of authigenic, idiomorphic barite microlites in a Typic Haplustult from Bellavista (Peru) is described on the basis of micromorphological and S.E.M. techniques. The microlites occur as clusters in the pores of the lower B and C horizons, which have slightly hydromorphic characteristics. These horizons are furthermore characterized by sepic plasmic fabrics and a strong fragmentation of most illuviation ferri-argillans, indicating conditions of repetitive swelling and shrinking. The fact that the microlites occur in voids, rather than having been incorporated in the s-matrix during the soil movements, suggests that they were formed after such movements and proves their authigenic character. They are presumed to be related to hydromorphic conditions and caused by saline groundwater. The microlites in the centres of the clusters have a tabular habit, composed of the following crystallographic forms: (001) (011) and probably (101). The others have a prismatic habit, composed of the same crystallographic forms, but dominated by (011) and elongated according to (001).