Volume 33, Issue 6 (November 1988)
Rapid Clay Mineralogical Analysis for Forensic Science Investigation—Clay Mineralogy Over the Short Distances
Rapid clay mineralogical analysis using a particle size fraction less than 0.05 mm without extraction of a clay fraction (< 0.002 mm) is applied to granitic soil samples collected from an area within a range of about 25 km with variation of topography. This area is located in a lucidophyllus forest climatic zone corresponding to a zone of yellow-brown forest soils. Clay mineralogical compositions obtained by this method showed different characteristics closely related to the topographic positions from where the soil samples were collected. It was confirmed that this method is effective for the discrimination of soil samples, and further for determining the original site of the soil samples as follows. In soils of hilly regions under well drained conditions, vermiculite is mixed with a large amount of gibbsite except for soil on flat places on ridges, which is characterized by the presence of a large amount of kaolin with a smaller amount of gibbsite. Soils under wet conditions such as valley-bottom plain and alluvial plain are characterized by interstratified clay minerals of chlorite and chloritized vermiculite. They are discriminated from each other in that the former are more abundant in gibbsite and the latter contain smectite.