File:Oolitic chert (Gatesburg Formation, Upper Cambrian; State College, Pennsylvania, USA) 2.jpg
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| Description |
English: Oolitic chert ("siliceous oolite") from the Cambrian of Pennsylvania, USA.
Oolitic rocks are composed of sand-sized (1/16 to 2 mm in size), well rounded, concentrically-layered grains called oolites (also known as ooliths or ooids). Most oolites are calcareous (CaCO3 - calcium carbonate - calcite or aragonite) and form by rolling back and forth on a shallow seafloor by wave action, or sometimes on a shallow lake bed. Oolites are forming today on the Bahamas Platform and in Great Salt Lake, Utah, USA. Oolitic rocks are usually limestones. Oolitic hematite, oolitic ironstone, and oolitic chert are also known. The sample seen here is oolitic chert from central Pennsylvania. Chert is a cryptocrystalline, quartzose sedimentary rock. Most have a chemical or biogenic origin. This one is a silicified oolitic limestone. Diagenetic or basinal fluids replaced the original calcium carbonate with micro- and cryptocrystalline quartz. This specimen, with blackish-colored oolites in a light-colored matrix, is the most noted variety of "siliceous oolite". Stratigraphy: Mines Member, upper Gatesburg Formation, Upper Cambrian Locality: unrecorded / undisclosed site at or near the town of State College, central Pennsylvania, USA |
| Date | |
| Source | https://www.flickr.com/photos/47445767@N05/53312538551/ |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/53312538551. It was reviewed on 7 November 2023 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 17:02, 7 November 2023 | | 3,142 × 2,289 (5.16 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/53312538551/ with UploadWizard |
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