Coprolite ?

[hndmarshall]

Found in gravel from the Brazos River ....I got it wet and it was a bit more tacky than other stones that given its odd shape and texture makes me think it may be Coprolite?... well one can hope right?...if its not that then it is some tacky poop looking concretion or normal stone....if it is nothing its another pebble for my garden of look like, could have been but nots.

[Rockwood]

I think this texture may be more related to a mineral that displays conchoidal fracture. I doubt it's a coprolite.

Someone should suggest that you try licking it though. 

[GeschWhat]

It could be a coprolite. It probably wouldn't be very tacky because the calcium phosphate would be in the form of apatite. The only really porous coprolites from Texas that I'm aware of are from the Eagle Ford Group. Yours has the right shape, texture and is from a fossiliferous area. I can't tell for sure, but there may be a surface inclusion peaking out in this photo (center right).