Dissolution process and rate in feldspar: Effects of crystallographic orientation.

Abstract

The effects of crystal orientation and dislocation density on the dissolution rates of feldspar (labradorite, Or2Ab44An54) were investigated, where three crystallographically different orientations were considered. The single crystal was prepared so as to have one predominant crystallographic face and then it was hydrothermally treated in acid solution at 90°C, 120°C and 150°C. The dissolution from (100) was the fastest of three orientations, and the rates of dissolution from (010) and (001) were almost the same. According to the SEM observations, small etch pits on (100) were arranged along two directions, and those on (010) and (001) were arranged along the cleavage. The dissolution on the plane normal to cleavage is faster than that on the plane parallel to it. Therefore, the microtextures such as cleavage and twinning play a more important role than the structural characteristics in the dissolution of labradorite.