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1.
J Forensic Sci ; 66(6): 2413-2423, 2021 Nov.
Article in English | MEDLINE | ID: mdl-34323303

ABSTRACT

The Natural Resources Conservation Service-Kellogg Soil Survey Laboratory has a large publicly available database of laboratory analyses of soil horizons collected from soil profiles largely from the United States. Among these soil properties are mineral grain counts from selected sand and silt fractions of soil horizons, performed by polarized light microscopy (PLM). These grain counts of over 20,000 fractions from 7534 sites provide a substantial reference that a forensic soil examiner could use to substantiate the rarity or commonness of a mineral species. The statement of the rarity or commonness of various minerals provide juries with additional context for the interpreting the results of a forensic soil comparison within the framework of a trial. The grain count data at specific locations can also be assessed to aid in soil provenance investigations, for cases where there are grain-counted sites in relevant locations. Two examples of application of these to data to soil evidence are included, one relating soil the rarity of a mineral (andalusite) to provide context in a soil comparison and one to aid in narrowing target regions in a soil provenance investigation.


Subject(s)
Minerals/analysis , Soil/chemistry , Forensic Sciences/methods , Geologic Sediments/analysis , Geology/methods
2.
J Forensic Sci ; 65(2): 438-449, 2020 Mar.
Article in English | MEDLINE | ID: mdl-31524965

ABSTRACT

Color determination of soil evidence is often done by visual comparison to soil color charts. A handheld spectrophotometer was tested with representative materials for its suitability for forensic soil characterization. Instrumental colorimetry provides accurate colorimetry with ~10-fold better precision than a soil color chart. The minimum sample size for accurate color determination was between 0.02 and 0.04 mg of fine soil for the specific instrument tested. Reporting colors in the L*a*b* space permits quantification of ΔE00 , a measure of perceptible color difference, could enable objective quantification of small color differences and thresholds for forensic soil comparisons. A ΔE00 greater than ~ 3.5 to 6 likely indicates disparate soil sources in a forensic comparison, in the absence of confounding factors like sample alteration. Despite the superior precision of instrumental colorimetry, this approach is inappropriate for samples which are mottled at an inseparable scale, attached to a substrate, or too small for instrumental measurement.

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