Abstract
Silica phytoliths are commonly found in hearths as a result of the combustion of plants. Their study in prehistoric hearths has enabled the identification of fire remains not visible to the naked eye due to the postdepositional processes. It has also enabled determination of the type of fuel used for the fires, and a better understanding of the functionality of hearths. However, little work has been done on understanding the combustion properties of fires and their relationship to the amount, distribution, and preservation of burned phytolith remains. We present here results of experiments carried out to shed more light on these questions. These results indicate that there are important differences in the combustion properties of fires. The remaining burned residues of the combustion depend on the use of naturally-dried or fresh fuel. These differences are related to the relationship between the presence of ash and charcoal fragments, the proportion of the acid-insoluble fraction, the amount and morphological distribution of phytoliths in the different fractions, and the refractive indices of the phytoliths. To recognize these properties it is essential to sieve the samples into different size fractions prior to the phytolith and mineralogical study. Postdepositional processes need to be taken into account as well when analyzing archaeological fire remains. The preference of one type of fuel over the other may have important implications related to the collection strategies and the proximity of available resources, as well as to the various possible uses of caves.