From my dad's shop. Is it a weapon or a tool?

Is it foam on the fat end? maybe some kind of a float? sump pump maybe?

The end is shaped rock. Limestone, I think. The handle is forged iron, definitely blacksmith style. It has no marks on the rock.

What size is it?  Random guess....window sash weight?

I wonder if it could be a bed warmer.  The ones I have had were flat pieces of soapstone with a wire handle.  They were heated on the stove and then rubbed on the sheets before you went to bed.

It is 12 inches long, and quite heavy. It has scraped areas on the stone, so I was wondering if it is something like a portable grind stone.

sandstone is common for grinding, limestone? no idea.

Could be sandstone. I'm not a geologist.

Could it be a fire lighter, my great uncle had something very similar, it has a piece of red brick on the end of it. He use to soak it overnight in a jar of kerosene, pull it out in the morning place it under some pine cones and light it up, the kerosene would burn for several minutes before it went out. the wire hand and brick were pulled out and stood alongside of the wood stove, then before bed he would take the lid off the jar and put it in there ready for the next morning. Cheers

Interesting concept. But wouldn't there be signs of scorching on the rock?

could it be for some type of weight for a fishing line, I'm no fisherman but it seems to me there were some nets and traps to catch some river / creek fish.

       
Dank is right. It comes with an iron pot and it is used for lighting a fireplace 

                    Its called a cape cod lighter.

Danks and jimandkc are correct. Also known as a fire starter.