Cooperative Extension Service

PETROGRAPHIC STUDIES


by Richard Drees

Single grain studies-detrital grains separated from the host material.

  1. Minerals can be separated according to size, speific gravity, or by magnetic gradients prior to study.
  2. Homogeneity and/or source of soil materials--determine ratios of minerals resistant to weathering, i.e., garnt/zircon, garnet/sphere, zircon/tourmaline, anatase/zircon, etc. Quartz grains are common, resistant and may have characteristics that are good indicators of source area and homogeneity.
  3. Weathering in place--ratio of weatherable to resistant materials, i.e., hornblend/zircon, biotite/tourmaline, etc.
Thin section studies--to observe soil constituents and their relationship to one another in their natural undisturbed arrangement. The structure or compostion of a soil can no more be determined from a crushed bulk sample than the architecture of a building from a pile of rubble.

  1. Observe fabric of soil, observe particle size and mineral distribution patterns, and local segregation of materials, i.e., clay on ped faces. Observe orientation patterns of soil material, and any special localized structural feature, i.e., nodules, pore fillings, pseudomorphs.
  2. Practical applications to soil disciplines include: permeability of clay liners to toxic wastes; effects of applied sewage sludges and amendments; soil corrosivity; soil structure, compaction, porosity, and crusting; archaeology and paleopedology; soil engineering; shear failure, soil strength and fault markers in soils; soil and mineral weathering; macropores and water movement; soil-root environment; soil biology; and soil genesis, classification and taxonomy.

    This page (http://www.ces.ncsu.edu/plymouth/programs/studies.html) created by
    Vera MacConnell, Research Technician, I on November 17, 1997.
    Last Updated on November 17, 1997.