Phytolith analysis

Phytoliths (from Greek, “plant stones”) are microscopic mineral plant particles that consist of hydrated silica (SiO2•nH2O). The silica is deposited in plants after absorption of silicic acid from the groundwater, which naturally contains silica because of erosion of minerals such as quarts and feldspar. While the water leaves the plant again due to evaporation, the silica is deposited in and between the plant cells. Phytoliths thus resemble plant cells. They may occur as single cells or in clusters.

Phytoliths offer two advantages compared to other archaeobotanical plant remains:
-since phytoliths are mineral plant remains, they remain preserved under a wide range of conditions (also after digestion and burning at temperatures up to 900 °C), and may thus offer information even when organic plants remains are not preserved;
-in contrast to seeds/fruits and pollen that represent the flowering parts of plants, phytolith assemblages can indicate the presence of various plant parts (chaff, leaves and stems). They can thus provide information that complements the information obtained from other archaeobotanical methods.

The application of phytolith analysis in archaeology may concern:
-the detection and identification of plant material such as chaff, leaves and culms in contexts such as food processing waste being part of refuse deposits, pottery temper and thatching or bedding material;
-an improved understanding of the function of archaeological features;
-in case of cereals: improved understanding of crop processing;
-the reconstruction of fuel use, for example wood versus grasses or wood versus dung;
-the reconstruction of diet by analysis of phytoliths from dental calculus, quern stones and coprolites.

Not all plants produce equally large quantities of phytoliths. Silica deposition in plants is particularly – but not exclusively– high in Monocotyledons such as grasses and sedges (including cereals), and in regions with a warm climate. Woody plants tend to produce relatively modest quantities of phytoliths.
The development of taxonomic identification criteria for phytoliths is a continuously ongoing process. Depending on the material under study, taxonomic identification of phytoliths is possible up to the level of family, subfamily, genus and/or species.

Simple instructions for phytolith sampling in the field are provided on the Archaeobotany wiki of Sheffield University. In case of sediment samples, c. 50 gram is enough. In case of dental calculus and food crusts also smaller samples are suitable for analysis. It is important to work under clean conditions to avoid contamination (comparable with pollen sampling), and to collect some control samples.

For more information, please contact:
Welmoed Out, PhD
wo(at)moesgaardmuseum.dk
T 87 39 40 41