When ammonite fossils are replaced by pryite, it can give them a Christmassy appearance. Pyrite replacement occurs in reducing, marine environments. When an organism decays, sulphide is released and reacts with dissolved iron in water to produce pyrite. This webpage gives a nice overview of how mineral replacement occurs.
| Accession Number | F0019 |
| Status | Accessioned |
| Specimen Type | Fossil |
| Brief Description | Ammonite |
| Full Description | One cut and polished half of a Dactylioceras tenuicostatum ammonite. Some chambers have been filled with calcite and pyrite and most of the inner walls/septa have been replaced by pyrite. From the Upper Lias |
| Quantity | 1 |
| Age (Ma) | 170 |
| Location | Whitby, North Yorkshire, England |
| Acquisition Method | Purchased |
| Acquisition Details | Festival of Geology, University College London – £5.00 |
| Acquisition Date | 2014-11-01 |
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