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Comparative Microscopy of Soil (1710)


Course schedule: 8:00 a.m. – 5:00 p.m. Monday – Thursday, and 8:00 a.m. – 12:00 p.m. Friday.

Students study the composition and origin of soils and approaches to scientific soil comparison by means of lectures, demonstrations and laboratory exercises. Small soil samples are literally taken apart and separated into clay, silt and sand size fractions, light and heavy minerals, and concentrates of pollen, spores, diatoms and phytoliths. At each stage appropriate methods of analysis are explained and demonstrated before the students conduct their own laboratory exercises. Interpretation of the result is based on geological and forensic principles which are explained as the students progress through the week. Proficiency in polarized light microscopy is assumed and necessary.

With respect to the individual components of soil, this is a survey course, dealing with comparative examinations and their interpretation.

Prerequisite: 1201 or equivalent

Day 1
• Comparative examinations vs. examinations for the purpose of developing investigative leads
• Historical and contemporary examples of cases in which soil examinations played a significant role
• Basic soil types and properties from the viewpoints of the geologist, mineralogist, soil scientist, and engineer
• Color, texture, particle size distribution and pH of soils
• Microchemical tests for soil cations, anions and pH
• Macroscopical and stereomicroscope examination of type soils
• Soil dissection, microchemical tests and pH determination
• Biological and anthropogenic components

Day 2
• Separation and isolation of soil fractions
• Technique for the separation of the sand and silt in Fraction 1
• Size and density separations of cleaned sand and silt
• Technique for mounting mineral grains for identification
• Review of optical crystallography, orientation determination and correlation of these properties in the identification of light minerals by polarized light microscopy
• Practice in the identification of known mineral grains

Day 3
• Recognition and identification of heavy minerals by polarized light microscopy
• The concept of mineral variety and its utilization in forensic soil comparison
• Additional techniques for mineral identification and their use and misuse in forensic soil studies
• Single grain manipulation, spindle stage, SEM/EDS, microchemical tests, FT-IR microspectroscopy, Raman microspectroscopy, X-ray diffraction

Day 4
• Separation and isolation of fractions 2, 3 and 4
• Separation and isolation of pollen, clay and aqueous fractions
• Introduction to the characterization and identification of pollen grains
• Recognition and identification of anthropogenic particles in fraction 2 such as combustion products, tire wear particles, etc.

Day 5
• Identification of clay and clay sized particles by optical crystallography, staining tests, FT-IR spectroscopy and X-ray diffraction
• Evidential value of clay identification and evaluation of the various techniques for the study of clays
• Analysis of the aqueous extract from the soil examination and its forensic value
• The evaluation and interpretation of soil evidence
• Understanding the parameters for a successful soil comparison
• The technique for tracing an unknown soil back to its origin or describing that origin
• Examples of comparison and sourcing