gravel from driveway rock/fossil?

[cpagak]

slightly larger than average piece of driveway gravel with heavy black lines and smears on both sides.  No indented fossils, but I wondered if this could be some sort of fossil from something.

[ClearLake]

I'm not recognizing any fossil in this.  What does the other side look like (always best to show both sides, that way we can see if the pattern is repeated or something totally different)?