Figure 1-5. Columnar calcite in a flowstone from an unnamed cave intersected by highway construction near Carthage, Tennessee, U.S.A. In this view in plane-polarized light, hardly any crystal boundaries are apparent (see red arrows for examples). A corresponding view in cross-polarized light is much more revealing. This particular calcite is enigmatic, but similar columnar crystals only a few millilmeters away appear to be the result of recrystallization.
     Photomicrograph was taken in plane-polarized light; field of view is 2.4 mm wide. Carthage, Tenessee, U.S.A.; Stalagmite MR68; thin section MR68. Sample collected from highway construction debris by L. Bruce Railsback.
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