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.
|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 Some chambers have been filled with calcite and pyrite and most of the inner walls/septa have been replaced by pyrite.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|
|Location||Whitby, North Yorkshire, England|
|Acquisition Details||Festival of Geology, University College London – £5.00|