Geo Advent Calendar Day 21

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.21-ammonite

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 Some chambers have been filled with calcite and pyrite and most of the inner walls/septa have been replaced by pyrite.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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