Soil survey laboratory grain count data to substantiate the rarity of mineral grains in forensic soil reports of examination

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.