Appears to have a thin layer of residual matrix over a bone fossil. However; this can also occur in geologic concretions or chert nodules found in limestone deposits. An X-ray scan of the specimen or in-person assessment will assist in identifying age and if the specimen is geologic or biologic in development.

From Images alone, I cannot give complete accuracy to your finding; but I do not disregard your research and the possibility that your example is a fossil. One aspect that gives me doubt: Most often a fossilized egg from these ancient eras will not break away from the ground/matrix it fossilized within. The organic matter of the earth and egg begin to fuse in most dinosaur egg examples. A churt or other mineral deposit will do so, because it is often surrounded by water or a less strong mineral that will allow it to break from the matrix it was surrounded by.

From Images alone, I cannot give complete accuracy to you finding; but I do not disregard your research and the possibility that your example does have biological materials.

“The Fossil Forum” is open to research and asking questions on fossils; the link will open to their dinosaur egg guide. While posing a question on the form is open to all responses; many are well researched and provide additional peer reviewed articles. http://www.thefossilforum.com

In person authentication, age, and origin will affect the possible value of this example. I do suggest you look to the fossil form and ask for an in-person assessment with a regional University Geology department or Natural History Museum. Often, these organizations will host experts in paleontology to review public finds. Researching current auction price results of Fossils; the expected fair market value would be in the range of 25 to 150 USD. With an in-person authentication to verify the specimens: a FMV could be achieved. It is important to recognize local, state, and US federal laws and prohibitions of sale and shipment of Fossils and Paleontology items.

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Hi,
This is an interesting example. To better help you, I need some additional information.
Where was this example sourced from? ie region
The location? ie riverbed, mountain side, creek, overturned in a pasture
An approximate weight?
Thank you, this information will help me guide you to learning more about this example and if it is biological or geological in origin.