When soil scientists and geologists cannot discern characteristics of soil particles and other Earth material with the naked eye, thin sections are prepared.

To prepare thin sections, undisturbed blocks of soil or other Earth material are filled with a glue, called epoxy resin, and are heated. Next, the blocks are allowed to harden and then placed in a block machine that saws off 1 cm diameter chips. A good specimen chip is selected and polished, then placed on a glass slide. The slide and the chip are placed in the thin section machine and are trimmed to 50 microns thick on the slide.

The slide is then placed on a wheel that finely abrades the glass slide and soil chip to 30 microns. It is at this point that light can successfully transmit from a special microscope through the 30 micron thin section. Thin sections containing minerals are particularly useful, as minerals have properties that can be seen only with high magnification and in certain light conditions. Soil contains minerals and by observing the optical properties of minerals in sand-sized grains, more accurate soil identification results. Here are some samples of thin sections:

Authigenic Kaolinite (in center), Carter Sandstone, Black Warrior Basin, Alabama

Authigenic Kaolinite, Carter Sandstone, Black Warrior Basin, Alabama



(Kaolinite micrographs courtesy of Ralph L. Kugler, Ph.D. Geology Section Milwaukee Public Museum)
 
 
 

Organic Components in Soil