# 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:** 2
**Author:** ![FloatyGimpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/floatygimpy/32/7750_2.png) [@FloatyGimpy](https://boards.straightdope.com/u/FloatyGimpy)\ **Post date:** [December 5, 2019, 3:36pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/21 "2019-12-05T15:36:50Z")
The posts about out of place rocks reminded me that, as a child, I saw some huge out of place rocks on one of the little island (Salt Spring, Pender or maybe Hornby) but I can’t find it now. I remember one of my classmates saying “a volcano exploded miles away and these rocks landed here”. It was one of those moments that really made an impression on me. It probably started my interest in rocks. I’m always finding rocks and bringing them home but just enjoyed looking at them. It’s very recently that I’ve wanted to know what they are. ---
**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 5, 2019, 4:41pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/22 "2019-12-05T16:41:15Z")
If it’s granite, it’s no coprolite (fossilized poop). As others have said, wave action subjects rocks to lots of abrasion, and causes rocks on the ocean shore to be nicely rounded. One way for a rock to end up _very_ round far away from an ocean is if it gets caught in a hole under a waterfall or the like. It gets continually tumbled and abraded about equally from all sides. > **[Making Marbles Out Of Rocks | Blind Pig and The Acorn](https://blindpigandtheacorn.com/making-marbles-out-of-rocks/)** > > how to make marbles from rocks ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 5, 2019, 4:49pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/23 "2019-12-05T16:49:37Z")
> [@FloatyGimpy](#): > > It fits perfectly in my hand. Enough so that it was very pleasant to carry. We’ve recently had a lot of rain and a tiny bit of snow. I think that some of the mud washed off of it so I was able to see it laying on the forest floor. Does it show any signs of wear or lots of small chipping/scratcing on one side or in a specific spot? ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [December 5, 2019, 4:50pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/24 "2019-12-05T16:50:35Z")
> [@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. Everything on the earth is old or recycled. Every breath of air you take has a statistical probability of including some molecules that Abraham Lincoln or Charlemagne or [Julius Caesar](https://www.sciencefocus.com/planet-earth/are-we-really-breathing-caesars-last-breath/) or Og the caveman also breathed. My teeny little mind finds that even more amazing. ---
**Author:** ![FloatyGimpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/floatygimpy/32/7750_2.png) [@FloatyGimpy](https://boards.straightdope.com/u/FloatyGimpy)\ **Post date:** [December 5, 2019, 5:34pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/25 "2019-12-05T17:34:30Z")
> [@Mangetout](#): > > Does it show any signs of wear or lots of small chipping/scratcing on one side or in a specific spot? It really does. It fits naturally in my right hand and at the bottom, slightly to the left, is a small, chipped out area. That area is also slightly discoloured. The whole rest of the rock is smooth. Here are a couple more pictures. You can see it in my hand and the area at the bottom. [![Imgur](https://live.staticflickr.com/65535/49174209447_a987154a75_b.jpg "Round3") ](https://www.flickr.com/photos/56821557@N06/49174209447/in/dateposted-public/) [![Imgur](https://live.staticflickr.com/65535/49174209737_0b63178cb8_b.jpg "Round4") ](https://www.flickr.com/photos/56821557@N06/49174209737/in/dateposted-public/) The reason I found it is my dog went to do her business about 30 feet off the trail in the underbrush. She’s had a little bit of diarrhea so I made my way over to where she went and saw it buried about halfway in the mud. ---
**Author:** ![txjim](https://avatars.discourse-cdn.com/v4/letter/t/f07891/32.png) [@txjim](https://boards.straightdope.com/u/txjim)\ **Post date:** [December 5, 2019, 5:41pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/26 "2019-12-05T17:41:46Z")
> [@Alessan](#): > > Could it be a geode? Crack it open and check. NO! What if it’s a Horta? ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [December 5, 2019, 5:48pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/27 "2019-12-05T17:48:04Z")
> [@FloatyGimpy](#): > > It fits perfectly in my hand. Enough so that it was very pleasant to carry. I know, right? I have a very smooth rounded river rock, sort of a somewhat flattened egg shape, fits my hand very well, and something about the size, shape, weight of holding it is–as you put it–very plesant for some unexplained reason. I wonder if hominids have some unexplored “like holding rocks” instinct? (I have lately been using it as a hammer stone on almonds and Brazil nuts with another, larger river rock as the anvil–which left no marks because the two stones didn’t hit each other, only the nuts.) ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 5, 2019, 5:48pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/28 "2019-12-05T17:48:08Z")
> [@FloatyGimpy](#): > > It really does. It fits naturally in my right hand and at the bottom, slightly to the left, is a small, chipped out area. That area is also slightly discoloured. The whole rest of the rock is smooth. Here are a couple more pictures. You can see it in my hand and the area at the bottom. > > [Round3 | cowardmelissa | Flickr](https://www.flickr.com/photos/56821557@N06/49174209447/in/dateposted-public/) > [Round4 | cowardmelissa | Flickr](https://www.flickr.com/photos/56821557@N06/49174209737/in/dateposted-public/) > > The reason I found it is my dog went to do her business about 30 feet off the trail in the underbrush. She’s had a little bit of diarrhea so I made my way over to where she went and saw it buried about halfway in the mud. It seems likely, or ar at least possible, that what you have there is a hammerstone ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [December 5, 2019, 5:59pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/29 "2019-12-05T17:59:32Z")
> [@CalMeacham](#): > > If it’s granite, it’s no coprolite (fossilized poop). But it could–in theory–have once been a gastrolith. Not _likely_, but _some_ dinos, at least, had them. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [December 5, 2019, 6:22pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/30 "2019-12-05T18:22:32Z")
> [@FloatyGimpy](#): > > It really does. It fits naturally in my right hand and at the bottom, slightly to the left, is a small, chipped out area. That area is also slightly discoloured. The whole rest of the rock is smooth. Here are a couple more pictures. You can see it in my hand and the area at the bottom. > > [Round3 | cowardmelissa | Flickr](https://www.flickr.com/photos/56821557@N06/49174209447/in/dateposted-public/) > [Round4 | cowardmelissa | Flickr](https://www.flickr.com/photos/56821557@N06/49174209737/in/dateposted-public/) > > The reason I found it is my dog went to do her business about 30 feet off the trail in the underbrush. She’s had a little bit of diarrhea so I made my way over to where she went and saw it buried about halfway in the mud. 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. ---
**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 5, 2019, 6:56pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/31 "2019-12-05T18:56:54Z")
> [@swampspruce](#): > > It’s also possible that it could be [gneiss](https://www.google.com/search?q=gneiss&client=firefox-b-d&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjL7Iqs6Z7mAhUSvVkKHU6qAHMQ_AUoAXoECBIQAw&biw=1920&bih=944#imgrc=_) or [amphibolite](https://www.google.com/search?client=firefox-b-d&biw=1920&bih=944&tbm=isch&sa=1&ei=UCLpXbS9NcfW5gLHi5D4Aw&q=amphibolite&oq=amphibolite&gs_l=img.3..0i67l4j0l6.136789.139853..140898...0.0..0.260.2830.0j2j11......0....1..gws-wiz-img.......0i131.DaaBqLRx1JQ&ved=0ahUKEwi0pfq-6Z7mAhVHq1kKHccFBD8Q4dUDCAY&uact=5) Nope (no foliation) and nope (not enough dark minerals) to both of those. ---
**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 5, 2019, 7:02pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/32 "2019-12-05T19:02:32Z")
> [@CalMeacham](#): > > One way for a rock to end up _very_ round far away from an ocean is if it gets caught in a hole under a waterfall or the like. It gets continually tumbled and abraded about equally from all sides. Just being in a fairly energetic river will do it. ---
**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 5, 2019, 7:03pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/33 "2019-12-05T19:03:35Z")
> [@FloatyGimpy](#): > > It really does. It fits naturally in my right hand and at the bottom, slightly to the left, is a small, chipped out area. That area is also slightly discoloured. The whole rest of the rock is smooth. Here are a couple more pictures. You can see it in my hand and the area at the bottom. > > [Round3 | cowardmelissa | Flickr](https://www.flickr.com/photos/56821557@N06/49174209447/in/dateposted-public/) > [Round4 | cowardmelissa | Flickr](https://www.flickr.com/photos/56821557@N06/49174209737/in/dateposted-public/) That does look like a hammerstone in those photos. ---
**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 5, 2019, 7:05pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/34 "2019-12-05T19:05:37Z")
> [@MrDibble](#): > > Just being in a fairly energetic river will do it. That’ll round off the edges and corners, but won’t necessarily make it _[round_. ---
**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 5, 2019, 7:07pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/35 "2019-12-05T19:07:44Z")
> [@Darren\_Garrison](#): > > But it could–in theory–have once been a gastrolith. Not _likely_, but _some_ dinos, at least, had them. Gastroliths are usually highly polished. ---
**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 5, 2019, 7:10pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/36 "2019-12-05T19:10:21Z")
> [@CalMeacham](#): > > That’ll round off the edges and corners, but won’t necessarily make it _[round_. No, it will. Not _spherical_, but rounded. The two being different things. ---
**Author:** ![whitetho](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whitetho/32/1059_2.png) [@whitetho](https://boards.straightdope.com/u/whitetho)\ **Post date:** [December 5, 2019, 9:30pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/37 "2019-12-05T21:30:10Z")
> [@txjim](#): > > NO! What if it’s a Horta? On Earth Horta’s would be considered an invasive species. We have enough problems with feral pigs, a colony of feral Horta’s, with their overaggressive mothers, would be significantly worse. ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [December 5, 2019, 11:01pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/38 "2019-12-05T23:01:27Z")
We already have the [Horta on earth](https://www.google.com/search?q=Pyura+chilensis&client=firefox-b-1-d&sxsrf=ACYBGNTS1B9UwMGhGwHTpYFfEAwUcGoUuw:1575586833685&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjAh6Oszp_mAhV0MX0KHXW4AdsQ_AUoAXoECBMQAw&biw=1760&bih=975&dpr=1.09). They’re more closely related to humans than they are coral or urchins or anything like that. ---
**Author:** ![FloatyGimpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/floatygimpy/32/7750_2.png) [@FloatyGimpy](https://boards.straightdope.com/u/FloatyGimpy)\ **Post date:** [December 6, 2019, 12:49am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/39 "2019-12-06T00:49:26Z")
> [@MrDibble](#): > > Gastroliths are usually highly polished. Man would I love to find one of those. I went for my evening walk and it took way longer than normal because I was picking up and looking at every rock. “Is that a Gastrolith??” Nope “Is _that_ a Gastrolith???” Nope… 😃 ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [December 6, 2019, 12:57am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/40 "2019-12-06T00:57:47Z")
I’ve wondered if any of [these](http://www.meteoriteguy.com/thuathe-hunt.htm) meteorites ended up as ostrich gastroliths. [Previous page](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386.md?page=1) [Next page](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386.md?page=3)