Not sure what this is, it's big and heavy, someone said petrified wood...but I'm not so sure.
I think it looks like petrified wood as well.
Remember, fossils have nothing to do with the original organic material. Fossilization, aka mineralization, will simply replace the fossil with its surrounding minerals. Since the process is extremely slow, there will be a difference between the surrounding rock, and the cavity it fills up (the cavity that once contained bone, which later rotted down to nothing), thus giving us the oportunity to tell rock and fossil apart. Some bodyparts will rot slower, such as hair and feathers, resulting in a different color in the resulting fossil, and the famous dark, fluffy outlines around feathered/furry fossils.
this means a fossil can be anything.
An obscure Australian fossil of the dinosaur
Kakuru is made of opal.