found this today

[RockinIdaho]

found this today just outside of town. about 3pp yards from plummer creek. walked a field

 

[Buckleberry]

Looks natural IMO.

 

[NCPeaches]

It looks like soapstone, is it super slick when it's wet?

 

[jamey]

you think it could of been a net weight?

 

[rock]

Leaverite stone

 

[Ponchosportal]

While the stone looks as if it may have been tied to something because of the groove; it is more likely less competent/vugey in that linear segment giving opportunity to easier erosion/degradation. Therefore it is a natural manifestation of the rock.