Interesting piece!

This rock appears to be a part of a nodule, possibly a concretion. These formations are often found in sedimentary rocks and are characterized by their rounded or irregular shapes, which are harder than the surrounding rock. The colors and textures suggest it could be a type of iron-rich nodule or a fossilized nodule.

Iron-rich nodules: These are often brown, red, or yellow due to iron oxidation. They can form in various environments, including soil, lake, or marine sediments.
Fossilized nodules: Sometimes, nodules can contain fossils, especially marine fossils, due to the way they form around organic material.
Concretions: These are hard, compact masses formed by the precipitation of mineral cement within sedimentary layers. They often have a different composition than the surrounding rock.

Given the appearance, it might be an iron-rich concretion or a fossilized nodule. For a more precise identification, examining it under a microscope or getting it analyzed by a geologist would be necessary.