Re-viewing raphides: Issues with the identification and interpretation of calcium oxalate crystals in microfossil assemblages

Abstract

Needle-shaped calcium oxalate crystals called raphides are increasingly being identified in microfossil assemblages from archaeological sites, including in sediments and as residues on artefacts. This paper reviews issues associated with the identification and interpretation of raphides in the archaeological record of the Pacific. It is argued that, with a better understanding of the occurrence, distribution, and morphological variability of raphides across higher plant families, more accurate and meaningful interpretations can be made of these archaeological microfossils. Problems with differentiating raphides from naturally occurring calcite crystals of similar morphology and optical properties are briefly raised and illustrated using the analysis of microscopic residues on Lapita pottery from sites in Melanesia.