thin section

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thin section A slice of a mineral or rock which is glued to a glass slide with resin of a particular refractive index (usually 1.540) and ground down to a thickness of 0.03 mm so that light may be transmitted through it when it is examined under a transmitted-light polarizing microscope. The mineral or rock chip is ground in successive stages, using carborundum or other suitable abrasives mixed with water, and when finished the section is covered with a glass cover slip, again attached with resin. This is the standard method for preparing most of the rock-forming minerals for study.