Figure 4-3. Microcrystalline calcite in the outer portion of a stalagmite. Note phosphate grain (P), quartz or feldspar grain (S), and other small detrital grains (arrows). "C" indicates more coarsely crystalline calcite. The presence of detrital grains within the microcrystalline calcite suggests that the calcite itself may be detrital in origin, but that hypothesis remains unconfirmed.      Photomicrograph was taken in plane-polarized light; field of view is 0.9 mm wide. Anjohibe Cave, Madagascar; Stalagmite MA3; thin section MA3-25; sample collected by Dr. George A. Brook.
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