Sand Compositional Analysis Using a Combined Geological and Spectroscopic Approach

Many minerals, such as calcite and magnetite, show diagnostic overtone and combination bands in the 350-2500 nm window. Sand, though an important unconsolidated material with great abundance on the Earth’s surface, is largely overlooked in spectroscopic studies. Over 100 sand samples were analyzed through traditional microscopic methods and compared to spectral reflectance collected via an ASD Spectroradiometer. Multiple methods were chosen to compare spectroscopic data to sand composition and grain size: 1) existing spectral indices, 2) continuum removal, 3) derivative analysis, and 4) correlation analysis. Particular focus was given to carbonate content. Results from derivative and correlation analysis showed strong correlations in the 2180-2240 nm and 2300-2360 nm windows to carbonate content. Proposed here is the Normalized Difference Carbonate Sand Index (NDCSI), which showed Pearson correlations of r=-0.78 for light-colored samples and r=-0.77 for all samples used. This index is viable for use with carbonate-rich sands.