A total of twenty 0-20cm soil samples from the El Yunque National Forest, Puerto Rico, have been analyzed using XRD analysis to determine their mineral content. Qualitative and quantitative analysis of the data show that all the samples contain quartz, orthoclase, kaolinite, dickite, halloysite and nicrite, gibbsite, augelite, metavariscite, goethite, tsaregorodtsevite, apophylite. Soil sample from Oxisols sites contain higher percentage of clay minerals than the samples from Dystrudepts sites. Furthermore, the general pattern of the percentage of total clays, feldspars, and gibbsite within each and between transects suggest that soils in the valleys are more weathered and leached than soils from ridges. The percentage increase of phosphate minerals in the soils follow that of clay minerals which is most probably due to the attachment of the phosphate minerals to clay mineral surfaces. The presence of the organic cation Tetramethylammonium in the cavities between the oxygen-silicon tetrahedra of the tsaregorodtsevite structure (feldsphoid-zeolitic structure) is consistent with a low energy mechanism for the sequestration of carbon and nitrogen in the EYNF soils.
Wang, Z. (2011): Mineralogy of Soils Overlying the Two Main Geologic Provinces of the El Yunque National Forest, Puerto Rico. University of Pennsylvania.