Optical mineralogy is a gaze turned deeply earthward into seeming dark, still, and silent depths. Indeed, when I first peered into a petrographic microscope in the Soil Science Laboratory of Colombia’s National Geographic Institute Agustín Codazzi (IGAC), I was slightly disappointed to find myself staring at what appeared to be an unassuming slice of magnified dirt. As soon as the polarizer filter was slipped into place, however, uniform darkness exploded into a kaleidoscope of fuchsias, yellows, violets, and blues. Odd shapes took form, mutated, and then disappeared as though enveloped back into a slowly churning color wheel. Hues shifted in intensity from shades of light to dark, more radiant and increasingly dull as the light diffracted mineral particles and the voids between them at different angles. The IGAC mineralogist who invited me to his workbench that morning registered my surprise, and reminded me that this was only the color spectrum detectable to the human eye. He went on to measure miniscule quartz grains and the size of clay minerals, and to note plant fragments and channels that indicate good oxygen flow and porosity. For me, this moment was akin to what renowned geographer and soil scientist, Francis D. Hole, described as the aesthetic “pleasures of soil watching.” For the mineralogist, his observations were important because they could alert to early signs of soil degradation or other ongoing structural damage caused by climatic forces that are increasingly difficult to disentangle from histories of human use and abuse. (read more...)