Rock with groove marks

[Bugzy99]

Found along the riverbank here in Maine....a triangular rock that I almost left (maybe I should have), took it home and cleaned it up slightly. With a magnifying glass it appear to have worn grooves, not natural on the end and just one side. Thoughts?

 

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[Icewing]

 

[trikikiwi]

IMO, sedimentary stone. Check out the shale in this link
Sedimentary Rocks | Pictures, Characteristics, Textures, Types

 

[Seek Ye First]

Perfect stone for skipping across a nice, still lake!! Betcha it'd go a loooooong ways too!

 

[TheCannonballGuy]

With super-enlargement, I see the un-natural perpendicular grooves in the sideview photo of the stone you found, and I agree, the edge looks un-naturally straight. I have no idea what it was used for.

 

[Goldfinger450]

Just a guess, but it may have been used as a sharpening stone, the grooves in the edge may be from using it to align the edge of a blade and possible that the stone was a slurry rock. I sharpen my own straight razors, knives etc and have a large number of sharpening stones of natural stone.