CLAY MINERAL IDENTIFICATION BY DIFFUSE SPECTRAL REFLECTANCE

Traditionally, the principle means of identifying clay minerals has been through X-ray diffraction (XRD). While effective, there are some disadvantages to using XRD for this application. XRD requires a good deal of sample preparation before measurements can be made. These sample preparation methods consume the sample in the process of doing the analysis. XRD instrumentation can also be expensive, a constraint which may place the technology out of the reach of some institutions.

As an alternative, we have explored the use of Diffuse Spectral Reflectance (DSR), as a means of eliminating these disadvantages. The method has been used extensively in satellite applications, but less so in marine sedimentology. Clay minerals have distinct spectral features, which make them relatively easy to identify with this method. The method is fast, non-invasive, and less expensive. With proper calibration the method can provide quantitative estimates of clay mineral concentration, rather than simple presence-absence estimates.

Using an Analytical Spectral Devices, LabSpec™ Pro FR we have developed a simple, and inexpensive means of constraining measurement geometry for use with its standard fiber optic probes. Our approach enables reproducibility of DSR measurements to better than 0.2% throughout much of the instrument’s measurement range which spans the UV/VIS/NIR from 350 –2500 nm. Replicate measurements of known clay mineral samples and fine grain separates (<63um) provide proof of concept.