Abstract
Grain size is a fundamental rock-forming characteristic of rocks that can be estimated under very different techniques. In this paper a simple and efficient 2-D stereological procedure for estimating the numerical density and the mean area of crystal sections as well as the area percentage of minerals in thin sections of rocks is presented. An example applied to the estimation of the mean section area and numerical density of the biotite crystals in a thin section of a tonalite is described in detail. Some results of the procedure application in a research project about Pink Porriño granite sawability are also presented.