Egg Shaped Rocks

[David N.]

I've been trying to figure out what these are off and on for several months, and while trying to get the background info straight, I think I may have stumbled a little closer to what they are.  I'm not sure this really belongs here now, but I'll post it anyway.  Feel free to move or delete it if it doesn't belong.

I had been detecting around where an old house had been on the property of one of my dad's neighbors.  A few days later, the man mentioned that these had been found in a field on another part of the farm and he wanted to know what these things that they described as "egg shaped rocks" are.  I don't know the quantity found other than "about a quart jar full" were found close together.  Someone told him they could be Native American game stones, while a geology professor told his son they were just some kind of rock that had weathered in a river somewhere.  I was skeptical about both, as apparently was he.

The best I can tell, the density of these is about 3.25 gram/cm^3.  I've only seen four of them, but apparently they are pretty typical of the others.  The size definitely isn't consistent, and they aren't perfectly round, but I think they are all in the range of roughly 1-1.5 inches diameter.  I'd searched for something this color and density, but couldn't find anything.  They seem pretty hard (coworker bounced one off of a tile floor), but I don't know much else about them property wise.

There is a creek within a few hundred feet of where they were found, and my dad mentioned that there used to be a mill on that creek.  That made me wonder if they were something related to the mill.  While searching, I did find some water filtration stones/balls that look very similar, but those appear to be two or three times as big as these.

Does anyone know what they really are?  Could they have been related to the mill?  Please let me know if there is anything else I can do to help identify them.

[jasong]

Look like water worn pebbles to me, but hard to know exactly out of context of the area.

If you want to determine the rock/mineral type then a scratch test is probably a good start, then go from there. See if you can make a tiny scratch in them with the tip of a steel knife. 

Offhand looks like some kind of limestone/dolomite or maybe even marble. 

[David N.]

I forgot to mention that these were found in south central Kentucky.  I don't know much at all about geology, but these are not similar to anything any of us have seen in this area.

When I try to scratch one of them, the knife leaves a mark, but it looks like the knife is leaving metal on it rather than scratching it.

[jasong]

Ok, that's some hard material then.

I'd guess porcelain/ceramic or alumina ball mill balls then.

[David N.]

The porcelain balls look pretty much identical to these.  How long have they been in use?  The mill was definitely gone by 1951, probably many years before that.  I thought the mill would have been for grinding corn or something like that, but these seem overkill for that.  What all would a ball mill have been used for?

[jasong]

I'm probably the wrong person to ask about old relic stuff, but I can say if they are ceramic that whatever they milled was softer than ceramic, which is about equal to quartz. Or, if they are alumina balls, they could have been milling something harder.

Probably could dive into some historic research on the old mill site and determine what they were milling. I'd probably start with chain of title and see if there is a company name somewhere on a deed.