| Ocala Chert: Petrology | |||||||||||
| Ocala Chert is colorless under plain polarized light and non- to weakly luminescent in CL, but some random limonite staining can be seen in some thin sections. That the chert formed through replacement of a former fossiliferous limestone by silica is clearly evident in thin section; "ghost fossils" are present in most specimens examined in this study. It is this petrographic characteristic that may permit resolution of Ocala Chert from other lithic materials in southeastern Alabama. The intensity of silicification is variable across hand specimens and thin sections. Samples are relatively soft where silicification was sporadic. Pervasively silicified specimens were replaced by cryptocrystalline chert. However, some replaced grains are bordered by a chalcedony cement or infilled by quartz suggesting later pore filling by secondary phases of silica. Non-silicified portions of this material contain numerous pores filled by calcite cement. The distribution of Ocala Chert in residuum suggests that it was concentrated through weathering. | |||||||||||
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| Typical cryptocrystalline texture of the Ocala Chert under plain polarized light. A diffuse brown mottling is responsible for some of the brown coloration of this material. Field of view approximately 0.5 mm. | Same view under crossed Nichols. Field of view approximately 0.5 mm. | ||||||||||
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| Numerous "ghost" fossils are preserved via silica replacement in Ocala Chert (as seen under plain polarized light). Void spaces are frequently filled by latter phases of chalcedony and quartz cement. Field of view approximately 1.0 mm. | Same view under crossed Nichols. Field of view approximately 1.0 mm. | ||||||||||