Figure 9-8. Calcite (C) with isolated areas of aragonite (A) that lie along the same layer in a stalagmite. C1 and C2 label individual columnar calcite crystals. A corresponding image shows the same area in plane-polarized light, and a high-magnification image shows the area in the red rectangle. The high-magnification image presents evidence that calcite has replaced aragonite, suggesting that the aragonite may have extended across the entire field of view of this image as one continuous layer, and perhaps suggesting that all the calcite (columnar and otherwise) in this image may have originated in replacement of aragonite.    Photomicrograph was taken in cross-polarized light with a gypsum plate in the light path; field of view is 2.3 mm wide. De Soto Caverns, Alabama, U.S.A.; Sample 95a; thin section 95a5. Sample collected by Dr. George A. Brook.
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