# 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:** 1
**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, 12:45am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/1 "2019-12-05T00:45:40Z")
Sorry - another rock question. I’m sure thousands of years ago, this rock was in the water and that’s how it ended up so round. But I found it deep in the forest, away from water sources. How did it get so round? How did it end up far away from water? And, most importantly, what kind is it?? It’s dry in the pictures. What are the tiny sparkles? [![Imgur](https://live.staticflickr.com/65535/49171112732_28cbc13865_b.jpg "Round2") ](https://www.flickr.com/photos/56821557@N06/49171112732/in/dateposted-public/) [![Imgur](https://live.staticflickr.com/65535/49170880666_0309de9c49_b.jpg "Round") ](https://www.flickr.com/photos/56821557@N06/49170880666/in/dateposted-public/) I want to put it in my aquarium but I know that the rock specialists/identifiers want the pictures to be dry. ---
**Author:** ![Ulfreida](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ulfreida/32/8014_2.png) [@Ulfreida](https://boards.straightdope.com/u/Ulfreida)\ **Post date:** [December 5, 2019, 12:54am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/2 "2019-12-05T00:54:14Z")
Looks like granite to me, but I’m no geologist. The shiny sparkles would be mica, I believe. Granite would be around 2 billion years old. A lot of stuff can happen in that period of time, I’m pretty sure. ---
**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, 1:00am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/3 "2019-12-05T01:00:32Z")
> [@Ulfreida](#): > > Looks like granite to me, but I’m no geologist. The shiny sparkles would be mica, I believe. **Granite would be around 2 billion years old**. A lot of stuff can happen in that period of time, I’m pretty sure. 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. ---
**Author:** ![Zeldar](https://avatars.discourse-cdn.com/v4/letter/z/b77776/32.png) [@Zeldar](https://boards.straightdope.com/u/Zeldar)\ **Post date:** [December 5, 2019, 1:02am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/4 "2019-12-05T01:02:56Z")
Somebody who knows those things much better than I do might help decide if it’s a > **[Coprolite](https://en.wikipedia.org/wiki/Coprolite)** > > A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is derived from the Greek words κόπρος (kopros, meaning "dung") and λίθος (lithos, meaning "stone"). They were first described by William Buckland in 1829. Before this, they were known as "fossil fir cones" and "bezoar stones". They serve a valuable purpose in paleo... There’s at least one photo that shows one that’s not what that name suggests! ---
**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, 1:07am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/5 "2019-12-05T01:07:11Z")
> [@FloatyGimpy](#): > > How did it get so round? How did it end up far away from water? And, most importantly, what kind is it?? I’m taking it for granite, too. As for how it got there, there are many theoretical possibilities, but given that you list your location as Vancouver Island, the answer is almost certainly “[dropped by a glacier](https://www.crd.bc.ca/education/our-environment/geology-processes/geological-history-vi).” ---
**Author:** ![Sunny\_Daze](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunny_daze/32/438_2.png) [@Sunny\_Daze](https://boards.straightdope.com/u/Sunny_Daze)\ **Post date:** [December 5, 2019, 1:38am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/6 "2019-12-05T01:38:54Z")
Granite! Dropped by a glacier works for me as well. ---
**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, 1:47am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/7 "2019-12-05T01:47:38Z")
Sounds like the consensus is glacier dropped Granite! If I remember my Vancouver Island history correctly, the last ice age did not cover the entire island, leaving a small area on the west coast uncovered. I think I remember that some Mammoths survived there. Fairly recently there was a ancient village found on one of the little islands along the west coast from 14,000 years ago which I think was when the last ice age here was ending. Amazing to think of what this rock has “seen”. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [December 5, 2019, 2:20am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/8 "2019-12-05T02:20:51Z")
A round rock found on an island might also have been shaped under water by the action of sand, gravel and wave action. ---
**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 5, 2019, 2:32am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/9 "2019-12-05T02:32:35Z")
I think the question has been answered and I agree. If the OP is interested, you can look for [glacial erratics](https://en.wikipedia.org/wiki/Glacial_erratic). These are large boulders that were plucked from a distant mountain during the ice ages and transported to some far away location, either by action of riding on or in a glacier, or on or in an iceberg, then dropped in their present location as the ice melted. They are composed of rock not found locally, and range up to house-size. The PNW is dotted with these. Here is one on [Vancouver Island](https://nwgeology.wordpress.com/the-fieldtrips/victorias-waterfront-geology-part-1-harling-point/). There is a pretty good picture showing the rock - it does not quite belong there. I think your cannon-ball rock probably traveled some distance, unless there is local granite that matches it. If that is the case, perhaps it was from a local river or creek and someone thought the same as you and transported from it’s source. In fact, being so polished makes me think that is more likely than being brought there by a glacier. Just speculating. ---
**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, 6:08am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/10 "2019-12-05T06:08:14Z")
> [@Darren\_Garrison](#): > > I’m taking it for granite, too. Someone stone this guy. ---
**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, 7:35am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/11 "2019-12-05T07:35:53Z")
Definitely granite-ish. Could be any one of a number of [related rocks](https://en.wikipedia.org/wiki/QAPF_diagram#/media/File:Qapf_diagram_plutonic_05.svg) depending on exact quartz percentage as well as the ratio of alkali feldspar to Plagioclase The twinkles _could_ be mica, could also be _schiller_ (iridescence) from the feldspars or just vitreous lustre from the quartz. ---
**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, 7:53am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/12 "2019-12-05T07:53:16Z")
How big is it? If it’s about the right size to fit in your hand and it was found completely out of place, there’s a possibility of it being a stone tool. We normally think of stone tools as appearing like pieces of flint, or obsidian, with sharp edges, but ancient humans also used round, hard stones as tools - for hammering or cracking nuts and seeds, for throwing weapons and weights, or for knapping flint (the toolset often includes a rounded rock for developing edges on the workpiece) here’s an example: [https://www.liveauctioneers.com/item/74057360\_stone-age-paleolithic-hammer-stone](https://www.liveauctioneers.com/item/74057360_stone-age-paleolithic-hammer-stone) Or, yeah, it could have been just a glacier drop, or left there for some reason by a modern human. ---
**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, 8:02am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/13 "2019-12-05T08:02:48Z")
> [@Mangetout](#): > > How big is it? If it’s about the right size to fit in your hand and it was found completely out of place, there’s a possibility of it being a stone tool. I don’t see any toolmarks on it at all. I doubt it’s a hammerstone. There’s not really any “out of place” applicable in a previously glaciated area. ---
**Author:** ![Alessan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alessan/32/465_2.png) [@Alessan](https://boards.straightdope.com/u/Alessan)\ **Post date:** [December 5, 2019, 8:11am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/14 "2019-12-05T08:11:20Z")
Could it be a geode? Crack it open and check. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [December 5, 2019, 8:43am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/15 "2019-12-05T08:43:42Z")
> [@Ulfreida](#): > > Looks like granite to me, but I’m no geologist. The shiny sparkles would be mica, I believe. Granite would be around 2 billion years old. A lot of stuff can happen in that period of time, I’m pretty sure. I’m not a geologist either, but I do know that granite has a much larger range of ages than that. The youngest granite appears to be this formation in Japan, which is only 800,000 years old. [https://www.nature.com/articles/srep01306](https://www.nature.com/articles/srep01306) ---
**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, 9:20am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/16 "2019-12-05T09:20:47Z")
> [@Alessan](#): > > Could it be a geode? Almost certainly not. ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [December 5, 2019, 9:41am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/17 "2019-12-05T09:41:33Z")
> [@eburacum45](#): > > I’m not a geologist either, but I do know that granite has a much larger range of ages than that. The youngest granite appears to be this formation in Japan, which is only 800,000 years old. > [Earth's youngest exposed granite and its tectonic implications: the 10–0.8 Ma Kurobegawa Granite | Scientific Reports](https://www.nature.com/articles/srep01306) My objection as well, but I agree with granite, mica, glacier or river and cool 🆒 Sure no geode, don’t break it. Probably no tool. ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [December 5, 2019, 3:24pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/18 "2019-12-05T15:24:23Z")
> [@snowthx](#): > > I think the question has been answered and I agree. > > If the OP is interested, you can look for [glacial erratics](https://en.wikipedia.org/wiki/Glacial_erratic). These are large boulders that were plucked from a distant mountain during the ice ages and transported to some far away location, either by action of riding on or in a glacier, or on or in an iceberg, then dropped in their present location as the ice melted. They are composed of rock not found locally, and range up to house-size. > > The PNW is dotted with these. Here is one on [Vancouver Island](https://nwgeology.wordpress.com/the-fieldtrips/victorias-waterfront-geology-part-1-harling-point/). There is a pretty good picture showing the rock - it does not quite belong there. I think your cannon-ball rock probably traveled some distance, unless there is local granite that matches it. If that is the case, perhaps it was from a local river or creek and someone thought the same as you and transported from it’s source. In fact, being so polished makes me think that is more likely than being brought there by a glacier. Just speculating. [This one](https://oregonstateparks.org/index.cfm?do=parkPage.dsp_parkPage&parkId=96) is a State Natural Site here in Oregon. I’ve been there. ---
**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, 3:30pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/19 "2019-12-05T15:30:34Z")
> [@Mangetout](#): > > How big is it? If it’s about the right size to fit in your hand and it was found completely out of place, there’s a possibility of it being a stone tool. > > We normally think of stone tools as appearing like pieces of flint, or obsidian, with sharp edges, but ancient humans also used round, hard stones as tools - for hammering or cracking nuts and seeds, for throwing weapons and weights, or for knapping flint (the toolset often includes a rounded rock for developing edges on the workpiece) > here’s an example: [https://www.liveauctioneers.com/item/74057360\_stone-age-paleolithic-hammer-stone](https://www.liveauctioneers.com/item/74057360_stone-age-paleolithic-hammer-stone) > > Or, yeah, it could have been just a glacier drop, or left there for some reason by a modern human. 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. ---
**Author:** ![swampspruce](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/swampspruce/32/261_2.png) [@swampspruce](https://boards.straightdope.com/u/swampspruce)\ **Post date:** [December 5, 2019, 3:34pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386/20 "2019-12-05T15:34:24Z")
If it was found near a walking path it’s also quite possible that it was transported to the forest by a L’il Hooman . My boys used to pick up and carry interesting rocks all the time when we’d take the dog out for her evening stroll. 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) but I’m going to take it for granite as well. 😃 If you’re a blossoming rock hound check out [www.geology.com](http://www.geology.com) for more than you ever wanted to know about what’s underfoot. [Next page](https://boards.straightdope.com/t/what-kind-of-rock-is-this-why-is-it-so-round/844386.md?page=2)