A preliminary study of acid volcanic rocks for stonemeal
#0183;#32;Fig. 1 shows the histograms of particle size distribution of the in situ samples in four granulometry ranges. These data show that residues from the extraction of basalt in the study region have different particle sizes, but all have a predominant particle size in the range of fine sand and silt; this influences the surface area, exposure of minerals, and, therefore, the release of nutrients.