Epi-fluorescent phytoliths: a proxy for fire?

Different methods have been applied to identify whether phytoliths have been heated: morphological alterations, changes in colour, refractive index (Elbaum et al., 2003) and Raman spectroscopy (Pironon et al 2001). As not all phytoliths seem to be affected in the same way, these methods obviously show their limitations. Besides the fact that some of them are quite difficult to apply on soil and sediment thin sections, none provide satisfactory results for sufficient discrimination between burned and unburned phytoliths (Evett and Cuthrell 2017).
Our observations of phytoliths in hearths and other combustion features revealed that phytoliths typically appear to be epi-fluorescent. First analyses show that this is probably related to the formation of a Ca-phosphorus-rich coating.
Further research on the origin and the formation of these coatings will be conducted to verify whether this technique can be used as a proxy for the heating of phytoliths.
References:
Elbaum, R., Weiner, S., Albert, R.M., Elbaum, M., 2003. Detection of burning plant materials in the archaeological record by changes in the refractive indices of siliceous phytoliths. Journal of Archaeological Science, 30, 217-226.
Evett, R. R. and Cuthrell, R.Q., 2017. Testing phytolith analysis approaches to estimate the prehistoric anthropogenic burning regime on the central California coast. Quaternary International, 434, 78-90.
Pironon, J., Meunier, J.D., Alexandre, A., Mathieu, R ., Mansuy, L., Grosjean, A., Jarde, E., 2001. Individual characterisation of phytoliths : experimental approach and consequences on palaeoenvironmental understanding. In : Meunier, J.D. and Colin, F. (Eds.), Phytoliths: applications in earth sciences and human history. A.A. Balkena Publisher, Lisse, pp. 329-341.