A TEST OF REFLECTANCE SPECTROSCOPY AS A PROXY FOR HEMATITE CONCENTRATIONS IN SYNTHETIC AND NATURAL SAMPLES

Sediment color is often used to quantify the abundance of weakly magnetic iron minerals, such as hematite or goethite in sediments and soils. Most studies, however, use mixtures of synthetic hematite and an iron-free matrix to calibrate the results of spectroscopic analyses. Such calibrations may be problematic as the color of hematite depends critically on crystallite size. We produced synthetic hematite using two methods outlined by (Schwertmann and Cornell, 1991) and produced standards with hematite concentrations ranging between 1 and 7 wt % and analyzed ten natural soil and sediment samples from New England, Iceland and Minnesota. Color analyses succeed in reconstructing hematite abundances in synthetic samples but yield semi-quantitative results at best for our natural sample set, allowing for the detection of relative changes in hematite abundance but making truly quantitative analyses problematic.

Schwertmann, U., and Cornell, R. M. (1991). "Iron Oxides in the Laboratory." VCH Verlagsgesellschaft, Weinheim.