It is very difficult to know if these are pieces of fossil leaf or not. The fact that some of the edges look like serrated edges to leaves could be coincidental.
With specialized equipment it would be possible to analyze the (very thin) dark patches. That could show they were of organic or inorganic origin. That will not be easy for us, however.
If you know where it came from (assuming it was not loose or not far from its outcrop), we could investigate to see if that contained (unambiguous) leaf fossils, then find photos to make comparison. Otherwise, we may never know; although they look like fossil plant fragments, that will probably remain merely our best guess.