BOTANICAL MUSEUM LEAFLETS VoL. 27, No. 5-6. 
May-JUNE 1979 
CHEMICAL TEST FOR SILICA DETERMINATIONS 
AS AN ARCHAEOLOGICAL FEATURE IN 
ETHNOBOTANY 
ELIZABETH A. COUGHLIN* 
Silica determinations of archaeological soils and ethnobotani- 
cal materials have consisted primarily of visual and microscopic 
identifications based on morphological measurements of dia- 
toms of sediment cores and of plant opal or phytoliths in the 
absence of other botanical evidence. 
Bacillariophyceae, or diatoms, are unicellular algae character- 
ized by a cell wall of silica, and classified on the basis of cell wall 
markings. Species are specific in their requirements and their 
relative abundance is useful in determining past environmental 
conditions. 
Phytoliths are opalline silica bodies found in the epidermal 
cells of certain plant groups. Unlike the silicification process in 
petrified wood, phytolith deposition produces distinct types 
associated with specific genera. 
Chemical analysis of archaeological soils and materials offers 
not only further substantiation for ethnobotanical identifica- 
tions, but also affords the possible mapping of a distinct 
archaeological zone consisting of silica deposition indicative of 
the past presence of standing or running waters, or of agricultur- 
al sites. 
A gravimetric determination of silica (as SiO.) can be meas- 
ured as loss on volatilization by means of hydrofluoric acid, 
after dehydration by use of both hydrochloric and perchloric 
acid. 
PROCEDURE 
1. PREPARATION OF SAMPLES 
A. Samples should be stored and tested in non-borosilicate 
containers, such as those of polyethylene, plastics or rubber. 
*Ethnobotanical Laboratory, Botanical Museum of Harvard University. 
161 
