Figure 3-4. A silica stalagmite consisting of generally randomly oriented chalcedony (A), a thick layer of large bundles of chalcedony (B), and a finely laminated zone of small bundles of chalcedony (C). The green arrow points to the sweeping extinction visible in the large bundles of chalcedony; the blue arrow points to one of the laminae in the small bundles. A corresponding view in plane-polarized light has the same red and blue labels but, but it's most striking feature is how little can be seen in it. Photomicrograph was taken incross-polarized light; field of view is 2.3 mm wide. Gaalweyte Cave, Somalia; Stalagmite GG2; thin section GG2F. Sample collected by Dr. George A. Brook.
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