What’s going on with this rock?

Being the dutiful soul that I am, I went to visit my 89 year old granddad earlier in the month. On a shelf in his living room, I found a curiously shaped rock with a hole right through the middle. When I asked him about it, he said he found it in his back yard (in North London) back in the 60s, and just kept it because he thought it was kinda cool. Well, he didn’t actually use the word “cool”, what with his being almost 90, he probably used a word more age-appropriate like “interesting” or “swell”, but the intent was much the same and I happen to agree. It is cool.

As such, I wonder if anyone can help identify what it is or how it could have been formed.

Pics are here:

Pic One
Pic Two
Pic Three
Pic Four
Pic Five

It is not clear from the pics, but the hole goes right through the stone and I can fit my little finger clean through it to the other side (sparking a minor panic when it didn’t come back out quite so easily).

So far I have come up with…

  1. It’s some kind of natural formation (a less robust rock was inside the rock and eroded away by water damage or something).

  2. It is what’s left of an old hammerhead. I note the smooth worn surface at the “point”. If so, any idea how old it might be? Victorian, Neanderthal or some modern cheapskate who bulked at the price of the hammers at B&Q?

  3. Something to do with insects. I noticed the holey/marked surface of the inside of the hole. You can’t trust insects, you know, they burrow.

  4. My granddad made it himself and is now just messing with my head in revenge for my laughing at him when he put the TV into power save mode last month and couldn’t figure out how to change it back for a fortnight

  5. Something else man-made related to grain grinding or sowing or something.

  6. Alien insects armed with hammers.

Any ideas?

Can’t see your pictures. I get “image blocked”.

I think you’ve got it right with your first suggestion. IANAGeologist.

I like the idea of a stone with a hole in it preventing become hag-ridden - that sounds like nothing but a good thing!

It looks quite a lot like a flint pebble - they often have holes or voids in them quite naturally.

I’d say it’s been part of a beach at some point in geological time.

Sometimes cavemen got lonely.

If the hole is human-made, it could be a stone sinker or net weight. It looks to me to be too small for a hammer or other hafted implement.

IANAGeologist, but I have (on extreeeeemly rare occasions) found small pebbles with holes in them. I always assumed natural, but if I find an arrowhead, I assume man-made, so go figure.

In between is glass, rubbed into shape by sand & waves. Always thought the source was manmade glass, but modified by nature.

There is a rock ledge not far from me that has larger rocks with small indentations in them, and in the summer, they fill with a red (algae?) coating. I suspect the depressions are natural but the algae are taking advantage of the area, which collects water. Perhaps the holes can get deeper?

My area is fresh water (Lake Michigan), so that might be a factor, compared to ocean salt.

Looking at some of the other pics, I’m certain it’s a flint cobble/pebble from a beach.

The shore near me - indeed along much of the South coast of England - is substantially composed of rocks just like that one (in shades of grey and orange-brown).

And the hole isn’t all that unusual - If you sit anywhere on the beach around here, there will be a stone like that within arms reach of you.

Thanks for the answers, all!

I wish I’d taken some better pictures, as I didn’t really catch how uniform the hole is, and where the wear is.

Pic Six

Looking at the nice smooth hole in Colibri’s link and the ragged poc-marked hole on this rock, it does look like it is more natural than man made. It is about the right shape for a very small hammer, and shows wear in the right places for a hammer, but the texture doesn’t seem right for man-made.

After reading the views here, my best guess would be that someone found a naturally “holed” stone on a beach, brought it up to London, and used it as a tool of some type (or just kicked it about a lot).

Mangetout - It is definitely the right size/shape/colour for having started life on a beach, so I’m sure you’re right there.

Zsofia - Sorry you can’t see it. I can probably upload them elsewhere if you’re really interested, but it’d probably be a bit of an anti-climax. After all, it’s a rock!

Thanks again, everyone.

I think I’ll print that link for the old man. He’ll like that! :slight_smile:

It might be just that the place they found it in London was once a beach (millions of years in the past)

This is almost certainly correct in my opinion. I have seen several of these stones with holes, in the Lower Columbia area of the Pacific Northwest USA. If Racer1 had said his location were North America I would say that it is a Native American fishing net weight.

Racer1, you said your location is North London. UK or Ontario?

If you found your rock near moving water, what most likely happened is that there were a few pebbles stuck on top of the rock. As moving water moves past your rock, it agitates the small pebbles that eventually erode a depression, eventually a hole, into the rock.

Holes like this in flint/chert pebbles are just part of the natural formation of the stone - it’s formed from the dissolved and recrystallised silica skeletons of ancient sponges and other invertebrates - sometimes the inner surface of the hole will bear an imprint of a fossil organism - other times, it’s just hollow, like a (not very pretty) geode.

If I can get to the beach this weekend, I’ll find some examples of similar stones.

The coin pictured alongside the stone is a UK 20p piece - I’m assuming this was found in the UK.

Yeah, London in the UK. Sorry, I should have specified.

FWIW, IANGeologist, and this explanation is probably correct. It’s a flint nodule that probably once also contained a Belmnite, which has since weathered away, leaving the hole.

I found a rock like that in a stream once. I think my brother still has it.