Diagnostic Methodology for Microinclusions in Objects of Soil and Geological Origin: Validation and Practical Application

Abstract This paper presents a microinclusions diagnostic methodology in objects of soil and geological origin developed on the basis of the Atlas of Microinclusions in Soils (hereinafter Atlas). The validation procedure methodology and an example of practical application are provided. The contents and structure of the Atlas, which describes 37 types of microinclusions, are described. Microinclusions are diagnosed using the Atlas key that represents a set of sequentially identified diagnostic features (transparency, shape, color, luster, fracture, structure, density, magnetic properties, hardness, and brittleness) typical of different types of microinclusions. The identification of a microinclusion (red brick) performed using the Atlas key is provided as an example. The validation procedure involves experimental verification of the testing reliability and evaluation of the reproducibility of test results under different conditions: samples of different complexity are examined by different experts at different times using different stereo microscopes. Seventeen samples that were previously (2–8 years ago) tested and kept as reference samples in the laboratory collection of site-collected samples were examined. Some soil samples were identified within the real casework, while others were identified within the framework of the interlaboratory proficiency test under the auspices of the European Network of Forensic Science Institutions (ENFSI). Two experts independently examined the reference samples at different times. It was established that the composition of the complex of microinclusions in each of the studied samples matched (by their types and number) the composition of the corresponding reference sample. The experts performed 108 tests with no erroneous results. This indicates the reproducibility of the test results and the competence of the experts. At the end of the paper, an example of practical application of the methodology is presented.