This is a slice of fossil dinosaur bone. Bone marrow tissues can be clearly observed.
In addition, its color is coincidental with that of the live bone marrow. As this fossil or petrified woods, there are fossils which we can observe the inside of original tissues in those polished surfaces.

Fossil Dinosaur Bone (120x10x6 mm)
Fossil Description: Unknown
Taxon: Utah, USA
Provenance: Jurassic
Formation: 165 Million Years Old