found these while collecting fossils by my house in Fort Worth Texas. They were buried along with the fossils and are fairly heavy for their size. Hoping someone can identify them for me Because there are more where those came from and I would like to know if collecting them would be worth my time. I have also included a pic of the common Fossils I find in that same area for comparison. Any info on those would be appreciated as well, I am a beginner. Thanks For your time guys have a great day
I think these could be coprolites.
Calcium phosphate is assocaited with coprolites, and they can also be pyritized.
Regarding their being 'fairly heavy for their size', high density could be due to:
- if only slightly 'heavy': calcium phospate (density 3.14g/ml vs. 2.71 for caclcium carbonate)
- considerably 'heavy': pyrite (~4.9g/ml)
Pyrite can occur as nodules, unrelated to poo. But such lumps can look rather similar.
The situation is confused further by pyrite specimens being more saleable/valuable if they are stated to be pyrite coprolites rather than pyrite nodules (I don't know why). Be aware of that when Googling 'pyrite coprolites'.
In most cases, we cannot determine what creature made a coprolite (the 'poopetrator'!).
You have a very nice assemblage in the 'associated fossils' (IMG_20140303_134058.jpg)
top - ammonite
top-left - oyster (possibly Gryphaea)
left - maybe brachiopod
bottom-middle-left - sea snail (gastopod)
bottom-middle-right - sea snail (gastropod, spirals largely still in stone)
right - bivalve or brachiopod
upper-right - can't tell - need more and closer photos
centre - sea urchin (echinoid)
Thank you so much for your insight for answer. Next time I go fossil collecting I will be Adding these to do list. I appreciate it so very much and hope you have a wonderful wonderful day
You're very welcome.
Nodules are certainly worth keeping an eye out for, especially dense ones. Some of those may be a dull brown or dark grey on the outside, but when you break them open, you may be rewarded with a sparkling display of metal-like ore. Marcasite nodules in particular come to mind. A Google image search will show you what I mean.
Good luck and fun,
Very good answer by Mike, as he mentioned pyrite associated with Coprolites I have attached an image of an Upper Lias - Lower Jurassic nodule that I split tonight, it was found on the Holderness coast.
You can see the coprolite, but there is a 'halo' of Pyrite around the nodule - less prominent is the Pyrite coating of the nodule.