A fragment of rock imbedded in another rock.
Geology is one of my first loves. I am a rock hound. In northwest Missouri, an amateur can find such fossils as clams, crinoids (sea lilies), petrified wood, and shark teeth.
My example of petrified poop isn't as photogenic as the 'egg'. But that is another story.
Any fellow Rock Hounds or budding Indiana Jones out there?