Any ideas on what type of rock this is?

What type of rock/stone (or possible relic?) could this be?

I have this peculiar looking rock thing. I live in Atlanta, Georgia, and when I was much younger, my uncle and I used to go on various fishing and hiking trips. I found this one day while we were fishing under a highway bridge that enters the local Stone Mountain Park. We basically went around to the side and underneath the bridge, which at that time was dirt and a very steep incline all the way down to the lake (it has since been paved on). I saw this rock kind of lightly buried into the dirt (it's not that much of a high traffic area and was difficult for some people to get to...not to mention a bit dangerous). So I presume that maybe the dirt on top washed down and exposed it and it might have been buried deeper before that land was developed to build the bridge in I guess early to mid 1900's. Or, someone more recent to that time "carved" it somehow.

It looks like an odd shaped long piece of rock (though the whole thing is just slightly longer than 1 inch). But one one side of it, it has these very sharp sides (6 flat sides) that go up into a point.

Any idea as to what it is? It is quite a hard rock, so I don't see how someone took something like a knife and "carved" it that way (as my uncle seemed to have thought). Yet it doesn't seem like a manual saw would be able to make shapes like this without cracking the rock or breaking off pieces. Only one of the flat "faces" on it that make the point seems to have a place on it where maybe a small amount of the rock minerals eroded away or something, but that looks natural.

Can anyone help? Thanks.

Here are some pictures that I took of it:

http://imageupper.com/g/?S020001008L13539712452548399