Is This A Sharpening Stone??

Before hunting with abarnard he had been gracious enough to bring me some AMAZING specimens to augment/improve my collection.  One of the coolest things I now have is a sandstone sharpening stone.  It is magnificent. 

I then saw a rock I had and wondered if it had a similar use.  I cannot tell if it is covered in iron from a fire but there are definitely some strange lines carved in to this rock.

Thank you ahead of time for any help.

Natural stone.

Here are a few pictures of the large slab of sharpening sandstone that was generously given to me.  When I place them side by side it becomes more apparent the first rock is natural.

This piece Adam gave me is the cat's meow!!  Thanks again!!!

Thank you for your response.  It is greatly appreciated.

Yes it is. Nice

  Nice one.

Was it found in a creek or a field, first one looks natural? I know the second one was given to you, it looks like disk strikes from tilling on the rock. I saw a lot of then in the fields of Missouri. Not saying it's not sharping stone, just that it looks like marks from field tiller.

My thought exactly Treasure Hunter. That second rock just looks like a piece of sandstone that has been abused by a plow.

The stone in the center of this tray is an actual Sharpening Stone.

There is a lot of old stuff that's going to remain mysterious no matter what. We don't have conceptual slots for it to fit into, so we dismiss it. But what we're really saying, when you come down to it, is that since we don't have any idea what it may have been, it must be nothing. And this in the face of the fact that, in many cases, it's something that somebody carried in from somewhere else (25-cent term : a "manuport") for some reason known to him but not to us.

Which still doesn't say anything about this one, one way or the other. But it does leave the door cracked, at least. 

Most sharping stones I have seen have deep groves from repeated sharping of points, while stones struck by farming equipment have random marks at different angles over the stone. Stones struck by tilling equipment may have marks start and stop in couple places if stone is large and have a gap in the middle of mark but marks line up with a ruler due to stone being uneven and or moving (sinking in ground or rolling along as it was struck.)

Again not saying it's not, only that it has all the characteristics of stone hit by disk tilling.

Granted !

The person who gave it to me is a geologist.  He has to travel to remote parts of Arizona for his job.  He said he has found four of these over the years in remote parts of Arizona.

I would be quite shocked if abusive plows were involved in the making of this rock. 

Either way I could care less whether a rogue plow did in fact go crazy in the Arizona desert.  I simply appreciate the gift and the thoughtful gesture.  Rogue plows aside.