heavy round rock found on beach in north west washington state

I found this 'rock' on the beach in North West Washington State.

It's almost perfectly round save for a few bumps, it's dark grey in colour, solid, feels smooth like any stone you'd find on the beach, and a little grainy in some places.
It's not metallic or magnetic, it's about a 6 on the hardness scale, and it's very heavy.
It seems to have 'seams' like natural cracks, but it's not frail.

Nothing chips off.

I just have no clue, and I'm worried that cutting it open to see what's inside might ruin whatever it is.

  • $\begingroup$ I don't know why this question got close votes, it has plenty of information. The only thing that was hidden in the image link was the location. I have edited the question. $\endgroup$ – Jan Doggen May 10 '19 at 18:40
  • $\begingroup$ Some kind of garnet crystal? If hardness > 6. $\endgroup$ – Lehs May 11 '19 at 11:22

What you have found is most likely a milling ball,You can probably find more of the same in the area where you found it.

Multiple balls are put in a rotating horizontal drum and the material you want to crush is slowly added to the drum.


The one you have found is probably made of granite but steel balls are more common now in modern mills.

I am not sure of what material your ball is made of so it can be any type of rock or it might be a man made material like ceramic.

Close to where i live was a cement factory and they used steel balls in the production,When the balls was worn out they where thrown out(they became excellent slingshot ammo).


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