The use of specific surface area, pore volume, and pore area in evaluating the degree of weathering of fine particles: an example from Lauhanvuori, western Finland

Abstract

Samples of weathered granite from the Lauhanvuori region, in western Fin­land have been collected in order to study the degree of weathering of the fine fractions in the weathering crust. Grain size distribution of the < 0.074 min diameter fractions has been determined by Sedigraph analysis. The nitrogen adsorption method has been used to determine the specific surface area of the fractions d < 0.02 min and < 0.074 mm, and the cumulative pore volume and pore area of the fractions < 0.074 min have been measured by using the mercury porosimeter test. The results obtained have been compared with those from materials for­med mainly by mechanical crushing by natural processes, such as the fine fractions present in silty till above the weathering crust in the Lauhanvuori area and a clayey vein filling in the regolith. They have also been compared with materials formed by artifical crushing, such as the powder from a gra­nitic aggregate. The fine‑grained material from the weathered deposits had specific sur­face area values of far greater than those corresponding from the silty till and the clayey vein. The results of the mercury porosimeter test showed a strong increase in the cumulative pore volume and pore area in pores with diameters < 1 um, as compared with the corresponding pore sizes in the finest powder of a similar grain size distribution from artificially crushed granite.