Microphotography of sample Los Vientos 123 with three different grain size distributions at 10x magnification. The left side is bright field mode (TLBF) and the right side is dark field mode (TLDF). The first row corresponds to the original sample; the second row is the sieved sample with particles in the range 38–45 μm; the last row is the sample milled 60–75 minutes with particles smaller than 10 μm. It is possible to observe a large fraction of small particles in the original sample. These small particles dominate the spectra compared to the larger particles. Therefore, the spectrum of the original sample is very similar to the spectrum of a milled sample with only small particles <10 μm.