This posting is not about a fossil but an interesting artifact I saw on display at the British Natural History Museum in London, England. It is called the Sunday Stone that formed in South Shields a Tyneside coal mine in the 1800s. A water trough in the mine used to relieve the thirst of work animals had the white mineral barium sulphate settle while container also had black coal dust accumulate during mining activity. It resulted in a banding and provides a visual representation of when the mining was going on (dark lines) and the white areas when it was Sunday (a day of rest) and larger gaps holidays or mine is idle.
Link to image of another one in the Oxford University collection:
https://www.geolsoc.org.uk/Geoscientist/Archive/August-2008/Never-on-a-Sunday
More information about Sunday Stones can be found in this book:
Curiosities of Natural History: Second Series by Francis T. Buckland 1903
https://archive.org/details/curiositiesnatu09buckgoog