# What kind of rock is this? Why is it so round? **URL:** \ **Category:** Factual Questions\ **Created:** [December 5, 2019, 12:45am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386 "2019-12-05T00:45:40Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![Isamu](https://avatars.discourse-cdn.com/v4/letter/i/7c8e57/32.png) [@Isamu](https://boards.straightdope.com/u/Isamu)\ **Post date:** [December 6, 2019, 1:12am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/41 "2019-12-06T01:12:59Z")
I went to a beach in the Tasmanian wilderness once where every rock (smaller than your head) was perfectly round. ---
**Author:** ![penultima\_thule](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/penultima_thule/32/3833_2.png) [@penultima\_thule](https://boards.straightdope.com/u/penultima_thule)\ **Post date:** [December 6, 2019, 2:16am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/42 "2019-12-06T02:16:01Z")
> [@FloatyGimpy](#): > > It just completely blows my teeny little mind that I can hold something in my hand that is that old. The carbon, hydrogen, oxygen, nitrogen, calcium etc atoms that compose the hand were created before that igneous rock was formed. As Joni Mitchell implied, we are all nuclear waste. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [December 6, 2019, 5:22am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/43 "2019-12-06T05:22:01Z")
> [@penultima\_thule](#): > > The carbon, hydrogen, oxygen, nitrogen, calcium etc atoms that compose the hand were created before that igneous rock was formed. It’s a statistical certainty that some of the calcium, at least, was once K[sub]40[/sub] much more recently than that. Still nuclear waste, though 🙂 ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [December 6, 2019, 12:34pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/44 "2019-12-06T12:34:58Z")
> [@MrDibble](#): > > No, it will. Not _spherical_, but rounded. The two being different things. We are quibbling over our own conceptions of the terminology ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [December 6, 2019, 2:48pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/45 "2019-12-06T14:48:11Z")
> [@CalMeacham](#): > > We are quibbling over our own conceptions of the terminology No, own conceptions doesn’t enter into it from my side. Both [roundness](https://en.wikipedia.org/wiki/Roundness_(geology))and [sphericity](https://en.wikipedia.org/wiki/Sphericity)are actual geological terms of art. And it’s possible to have high sphericity and low roundness. Geology can be weird that way. ---
**Author:** ![Nars\_Glinley](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nars_glinley/32/8177_2.png) [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)\ **Post date:** [December 6, 2019, 4:03pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/46 "2019-12-06T16:03:53Z")
> [@FloatyGimpy](#): > > It just completely blows my teeny little mind that I can hold something in my hand that is that old. I find rocks incredibly fascinating. 10% of your body is over 13 billion years old. ---
**Author:** ![Dana\_Scully](https://avatars.discourse-cdn.com/v4/letter/d/5daacb/32.png) [@Dana\_Scully](https://boards.straightdope.com/u/Dana_Scully)\ **Post date:** [December 6, 2019, 4:09pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/47 "2019-12-06T16:09:19Z")
> [@FloatyGimpy](#): > > It just completely blows my teeny little mind that I can hold something in my hand that is that old. I find rocks incredibly fascinating. me too :eek: science is so…fascinating. I wish I could think of a better word to describe it. It IS mind-blowing that we humans can co-exist with something that’s so…old! ---
**Author:** ![Ignotus](https://avatars.discourse-cdn.com/v4/letter/i/ecc23a/32.png) [@Ignotus](https://boards.straightdope.com/u/Ignotus)\ **Post date:** [December 6, 2019, 5:00pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/48 "2019-12-06T17:00:18Z")
> [@MrDibble](#): > > Just being in a fairly energetic river will do it. Yeah, and if the river happens to be flowing through a tunnel or crevasse in a glacier, the rubble will typically end up as an [esker](https://en.wikipedia.org/wiki/Esker)when the glacier is gone; somewhat counter-intuitively with the coarser stuff deposited on top of the finer sand! [Rullstensås – Wikipedia](https://sv.wikipedia.org/wiki/Rullstens%C3%A5s#/media/Fil:Rullstens%C3%A5s_i_genomsk%C3%A4rning.JPG) ---
**Author:** ![crowmanyclouds](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crowmanyclouds/32/19884_2.png) [@crowmanyclouds](https://boards.straightdope.com/u/crowmanyclouds)\ **Post date:** [December 6, 2019, 9:05pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/49 "2019-12-06T21:05:25Z")
I have about half a dozen of these, none as large as the OP’s. The first was found in my grandparents garden. In a town that never had any serious industrialization, so my guess that it might have been used in a ‘ball mill’ seems unlikely. However said town is on the terminal moraine of the last ice age. I’ve found a couple in the rocks they put in parking lots instead of plants. > [@Darren\_Garrison](#): > > But it could–in theory–have once been a gastrolith. Not _likely_, but _some_ dinos, at least, had them. > > > [@MrDibble](#): > > > > Gastroliths are usually highly polished. Also, [gastroliths ain’t exactly round](https://www.google.com/search?q=gastroliths&newwindow=1&source=lnms&tbm=isch&sa=X&ved=2ahUKEwijlbby9aHmAhUOjlkKHZb6A14Q_AUoAXoECG0QAw)! CMC fnord! ---
**Author:** ![snowthx](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snowthx/32/10660_2.png) [@snowthx](https://boards.straightdope.com/u/snowthx)\ **Post date:** [December 7, 2019, 12:40am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/50 "2019-12-07T00:40:05Z")
> [@Dallas\_Jones](#): > > It seems likely that this is a human tool of some kind. Either shaped by hand or found and modified. Vancouver Island is a very resource rich environment and there were large populations of indigenous people there for thousands of years. I was thinking about this as well. Where I live there are many places where the Native Americans, or, ahem First Nation people ground various food items, using favorite rocks as a pestle - once such as the OP, used for a long time, would become round, and as stated, fits nicely in the hand. Perhaps the rock is a grinding stone? Not sure if that activity or food prep was common on Vancouver island. ---
**Author:** ![The\_Stafford\_Cripps](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_stafford_cripps/32/7167_2.png) [@The\_Stafford\_Cripps](https://boards.straightdope.com/u/The_Stafford_Cripps)\ **Post date:** [December 7, 2019, 9:58am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/51 "2019-12-07T09:58:20Z")
In my opinion there is no reason to think that the stone’s shape isn’t natural. You can find lots of very rounded stones like it on a pebbly beach, especially when the rock isn’t stratified. It might have been carried to the find spot by humans, but I’d want to rule out local morraine as a source. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [December 7, 2019, 10:33am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/52 "2019-12-07T10:33:53Z")
There are beaches on Lake Michigan entirely made of such stones. If you are going to claim they were tools used by generations past, the population must have been enormous and they must have been doing a heckovalotta pounding. More likely, they are a product of nature. A rounded stone near a lake or river or in a glacier’s path is about at natural as I can ever imagine. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [December 7, 2019, 12:18pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/53 "2019-12-07T12:18:29Z")
I don’t think anyone’s saying that the rock was rounded by people, just that it looks like the already-rounded rock was used as a tool. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [December 7, 2019, 12:24pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/54 "2019-12-07T12:24:26Z")
> [@crowmanyclouds](#): > > Also, [gastroliths ain’t exactly round](https://www.google.com/search?q=gastroliths&newwindow=1&source=lnms&tbm=isch&sa=X&ved=2ahUKEwijlbby9aHmAhUOjlkKHZb6A14Q_AUoAXoECG0QAw)! Except those [goose gastoliths](https://www.projectnoah.org/spottings/8301489). Damn, those are pretty. ---
**Author:** ![The\_Stafford\_Cripps](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_stafford_cripps/32/7167_2.png) [@The\_Stafford\_Cripps](https://boards.straightdope.com/u/The_Stafford_Cripps)\ **Post date:** [December 7, 2019, 12:45pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/55 "2019-12-07T12:45:42Z")
> [@MrDibble](#): > > I don’t think anyone’s saying that the rock was rounded by people, just that it looks like the already-rounded rock was used as a tool. It certainly looks to us armchair archaeologists like it could be used as a tool of some kind, but what we’re pointing out is that there is a vast number of pebbles like it in the world that have never been used as a tool, and so the odds are against it. An expert would be able to tell if there are marks on the stone that indicate tool use (though would they be able to distinguish marks from 4000 years ago from marks from 40 years ago?) But you’d really have to look at the soil/moraine it came from to assess probabilities. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [December 7, 2019, 1:09pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/56 "2019-12-07T13:09:47Z")
When I was a kid tooling around in the high desert on motorbikes with my cousins, one of them found this nearly round piece of obsidian and gave it to me. (I’d call it “egg shaped” except that it’s rounder than that. No “pointy” end.) I still have it. A student with a rock tumbler offered to smooth it out for me (it had a sand coating on part of it) but it turned out to be snowflake obsidian and that wouldn’t work. If a glass-like substance like obsidian can get fairly round naturally, I have no problem with a granite-like rock being rounder. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [December 7, 2019, 1:47pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/57 "2019-12-07T13:47:44Z")
> [@The\_Stafford\_Cripps](#): > > what we’re pointing out is that there is a vast number of pebbles like it in the world that have never been used as a tool …and so wouldn’t have wear marks. > [@](#): > > would they be able to distinguish marks from 4000 years ago from marks from 40 years ago? In some cases, yes. Stuff like degree of weathering on exposed surfaces in the wear marks, or analysis of organic material in them. There’s a couple of disciplines devoted to this, called microwear analysis and use-wear analysis. ---
**Author:** ![The\_Stafford\_Cripps](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_stafford_cripps/32/7167_2.png) [@The\_Stafford\_Cripps](https://boards.straightdope.com/u/The_Stafford_Cripps)\ **Post date:** [December 7, 2019, 2:09pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/58 "2019-12-07T14:09:46Z")
I’d overlooked the OP’s comment on possible wear marks above. We’d still want to get an idea of aging (googling ‘granite patina’ doesn’t help much!) and to rule out natural or modern day causes of the abrasions. ---
**Author:** ![chela](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chela/32/21582_2.png) [@chela](https://boards.straightdope.com/u/chela)\ **Post date:** [December 7, 2019, 2:24pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/59 "2019-12-07T14:24:41Z")
Neat stones catch my eye too, I"ve found a few small tools, unifaces, preforms, small points, paleoindian possibly. THere are a few online forums where you can learn about pre-columbian tools etc. Generally good info if your willing to search and wade through the forums. [https://forums.arrowheads.com/](https://forums.arrowheads.com/) [http://www.treasurenet.com/forums/north-american-indian-artifacts/](http://www.treasurenet.com/forums/north-american-indian-artifacts/) If you want to show your rock, get good clear close ups just don’t say it fits in thehand therefore it must be a tool that seems to trigger some of those guys in to yelling. But lots of info and pictures of other similiar rocks to make comparisons with and decide what you have is a tool or just a rock. ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [December 7, 2019, 2:29pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/60 "2019-12-07T14:29:24Z")
> [@MrDibble](#): > > I don’t think anyone’s saying that the rock was rounded by people, just that it looks like the already-rounded rock was used as a tool. Space aliens?:eek: Seriously, it looks like any old rock you might find in or around streams and rivers and whatnot. [Previous page](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386.md?page=2) [Next page](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386.md?page=4)