# What's up with this rock? **URL:** \ **Category:** Factual Questions\ **Created:** [January 18, 2015, 5:59am UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140 "2015-01-18T05:59:38Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [January 18, 2015, 5:59am UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/1 "2015-01-18T05:59:38Z")
I picked up this rock on the beach at [Koh Libong](https://maps.google.co.th/maps?q=koh+libong&oe=utf-8&client=firefox-a&channel=sb&hnear=Ko+Libong&t=h&z=13), an island on the South of Thailand, the region has lots of Karst type formations but the rocks there looked different, dark red mostly and with lots of banding and inclusions (correct me if I am wrong in the terminology, I’m just a step above zero level in geology) Anyway, some pictures, I rinsed it to make the colours and details stand out more, the grid is 1cm squares: [Pic 1](https://picasaweb.google.com/lh/photo/L_2JPoz2t5ndBP7FfMCCpRe5vDPciyXd0zJplGyX-t4?feat=directlink) [Pic 2](https://picasaweb.google.com/lh/photo/9cYgDrzrSoUMpIDMMECY7Be5vDPciyXd0zJplGyX-t4?feat=directlink) [Pic 3](https://picasaweb.google.com/lh/photo/z7b21SAgGwbtLZfP_QD7dBe5vDPciyXd0zJplGyX-t4?feat=directlink) I don’t recall ever seeing something like this (although there were many similar rocks on the beach), I guess it’s some type of limestone stained by iron for the red, but that’s all I could venture. ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [January 18, 2015, 6:26am UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/2 "2015-01-18T06:26:06Z")
> [@Ale](#): > > [Pic 1](https://picasaweb.google.com/lh/photo/L_2JPoz2t5ndBP7FfMCCpRe5vDPciyXd0zJplGyX-t4?feat=directlink) You can’t fool me; that’s a moldy potato. ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [January 18, 2015, 6:43am UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/3 "2015-01-18T06:43:29Z")
> [@tomndebb](#): > > You can’t fool me; that’s a moldy potato. You obviously don’t know your geology. That’s a yam. ---
**Author:** ![GIGObuster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gigobuster/32/421_2.png) [@GIGObuster](https://boards.straightdope.com/u/GIGObuster)\ **Post date:** [January 18, 2015, 6:46am UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/4 "2015-01-18T06:46:10Z")
Looks to me like red sandstone with mineral deposits. In larger quantities, with that kind of deposit, one could get something like the Danxia Landforms from China. [http://reversehomesickness.com/asia/landforms-in-china-zhangye-danxia-mountains/](http://reversehomesickness.com/asia/landforms-in-china-zhangye-danxia-mountains/) ---
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [January 18, 2015, 6:47am UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/5 "2015-01-18T06:47:14Z")
Looks like some sort of metamorphic rock to me. Interesting, but not uncommon. ---
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [January 18, 2015, 6:50am UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/6 "2015-01-18T06:50:23Z")
> [@GIGObuster](#): > > Looks to me like red sandstone with mineral deposits. > > In larger quantities, with that kind of deposit, one could get something like the Danxia Landforms from China. > > [http://reversehomesickness.com/asia/landforms-in-china-zhangye-danxia-mountains/](http://reversehomesickness.com/asia/landforms-in-china-zhangye-danxia-mountains/) That can’t be real, can it? It’s too beautiful to have never been seen (by me) before. ETA: Damn. I Googled it, and it’s more beautiful than imaginable. ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [January 18, 2015, 7:07am UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/7 "2015-01-18T07:07:51Z")
> [@GIGObuster](#): > > Looks to me like red sandstone with mineral deposits. > > In larger quantities, with that kind of deposit, one could get something like the Danxia Landforms from China. > > [http://reversehomesickness.com/asia/landforms-in-china-zhangye-danxia-mountains/](http://reversehomesickness.com/asia/landforms-in-china-zhangye-danxia-mountains/) Ooh… pretty. _makes new entry on the “Places to go to” list_ Yes, it feels like sandstone, but throughout the area most other islands are made of limestone from ancient reefs. ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [January 18, 2015, 7:33am UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/8 "2015-01-18T07:33:27Z")
> [@tomndebb](#): > > You can’t fool me; that’s a moldy potato. Shush!, let them scramble a bit first. 😃 ---
**Author:** ![straight\_doped](https://avatars.discourse-cdn.com/v4/letter/s/49beb7/32.png) [@straight\_doped](https://boards.straightdope.com/u/straight_doped)\ **Post date:** [January 18, 2015, 9:32am UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/9 "2015-01-18T09:32:43Z")
> [@Ale](#): > > I picked up this rock on the beach at [Koh Libong](https://maps.google.co.th/maps?q=koh+libong&oe=utf-8&client=firefox-a&channel=sb&hnear=Ko+Libong&t=h&z=13), an island on the South of Thailand, the region has lots of Karst type formations but the rocks there looked different, dark red mostly and with lots of banding and inclusions (correct me if I am wrong in the terminology, I’m just a step above zero level in geology) > > Anyway, some pictures, I rinsed it to make the colours and details stand out more, the grid is 1cm squares: > > [Pic 1](https://picasaweb.google.com/lh/photo/L_2JPoz2t5ndBP7FfMCCpRe5vDPciyXd0zJplGyX-t4?feat=directlink) > [Pic 2](https://picasaweb.google.com/lh/photo/9cYgDrzrSoUMpIDMMECY7Be5vDPciyXd0zJplGyX-t4?feat=directlink) > [Pic 3](https://picasaweb.google.com/lh/photo/z7b21SAgGwbtLZfP_QD7dBe5vDPciyXd0zJplGyX-t4?feat=directlink) > > I don’t recall ever seeing something like this (although there were many similar rocks on the beach), I guess it’s some type of limestone stained by iron for the red, but that’s all I could venture. what does it taste like? ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [January 18, 2015, 10:18am UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/10 "2015-01-18T10:18:40Z")
> [@straight\_doped](#): > > what does it taste like? Hey, I just had a dental impression done last Friday, I don’t want to pay for a second, updated, one. ---
**Author:** ![chiroptera](https://avatars.discourse-cdn.com/v4/letter/c/df705f/32.png) [@chiroptera](https://boards.straightdope.com/u/chiroptera)\ **Post date:** [January 18, 2015, 10:25am UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/11 "2015-01-18T10:25:13Z")
I googled _rocks that look like sweet potatoes_ and found the [Potato Rock Museum](http://www.potatorock.com/html/museum.html). Seems like you found a piece of [chalcedony quartz](http://en.wikipedia.org/wiki/Chalcedony). ---
**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:** [January 18, 2015, 12:48pm UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/12 "2015-01-18T12:48:20Z")
It looks a bit like it could have been altered by the heat of a beach fire - is that a possibilitiy? You say there were others like it on the beach - were the rocks like this clustered at all? ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [January 18, 2015, 1:14pm UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/13 "2015-01-18T13:14:51Z")
> [@Mangetout](#): > > It looks a bit like it could have been altered by the heat of a beach fire - is that a possibilitiy? You say there were others like it on the beach - were the rocks like this clustered at all? No, just scattered all along the beach, although most of them were dark red to purplish, same as the larger rock formations, and on those I didn’t see any patterns like on this one; there was however an outcrop with thin (2 to 5mm) veins of a crystalline white material, quartz maybe. ---
**Author:** ![scoots](https://avatars.discourse-cdn.com/v4/letter/s/b77776/32.png) [@scoots](https://boards.straightdope.com/u/scoots)\ **Post date:** [January 18, 2015, 1:54pm UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/14 "2015-01-18T13:54:59Z")
I’m not convinced those rocks in China really look like that in real life. I’m wondering about filtering being used etc. Here’s a youtube vid. They’re still pretty and they are colourful and maybe on a really bright sunny day they would take on even more colour but they don’t look like a Van Gogh painting [![](https://img.youtube.com/vi/vUkM869X4ik/maxresdefault.jpg "Zhangye Danxia Landform 張掖丹霞地貌 2014 short") ](https://www.youtube.com/watch?v=vUkM869X4ik) ---
**Author:** ![Mr.Miskatonic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mr.miskatonic/32/310_2.png) [@Mr.Miskatonic](https://boards.straightdope.com/u/Mr.Miskatonic)\ **Post date:** [January 18, 2015, 2:10pm UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/15 "2015-01-18T14:10:10Z")
Mookaite? (you’ll have to google it yourself, I can’t seem to get an URL.). ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [January 18, 2015, 2:31pm UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/16 "2015-01-18T14:31:59Z")
> [@Mr.Miskatonic](#): > > Mookaite? (you’ll have to google it yourself, I can’t seem to get an URL.). The colors look spot on, but I don’t know if mine could be polished as I see in the image search; it would look really nice though!. From this wiki entry ([Radiolarite](http://en.wikipedia.org/wiki/Radiolarite)) it seems to be sedimentary and marine in origin, but as I said the texture on my rock is more like sandstone/limestone than what I see in the pictures, but then again I found it on the shore so it’s been roughed up by the sand. Any suggestions on polishing without a rock tumbler? ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [January 18, 2015, 2:38pm UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/17 "2015-01-18T14:38:32Z")
[quote=“scoots, post:14, topic:710140”] I’m not convinced those rocks in China really look like that in real life. I’m wondering about filtering being used etc. Here’s a youtube vid. They’re still pretty and they are colourful and maybe on a really bright sunny day they would take on even more colour but they don’t look like a Van Gogh painting [/QUOTE] I’m sure the more vivid photos had their colour saturation cranked up to eleven. Still looks gorgeous in the more subdued ones too. ---
**Author:** ![Mr.Miskatonic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mr.miskatonic/32/310_2.png) [@Mr.Miskatonic](https://boards.straightdope.com/u/Mr.Miskatonic)\ **Post date:** [January 18, 2015, 2:54pm UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/18 "2015-01-18T14:54:10Z")
> [@Ale](#): > > Any suggestions on polishing without a rock tumbler? Lots of sandpaper. And maybe a Dremel. ---
**Author:** ![elbows](https://avatars.discourse-cdn.com/v4/letter/e/b3f665/32.png) [@elbows](https://boards.straightdope.com/u/elbows)\ **Post date:** [January 18, 2015, 3:07pm UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/19 "2015-01-18T15:07:47Z")
Hey, I picked up some of these same rocks when I was in the same region last year. They are very cool. ( I had already acquired considerable seashells, and so was resisting the urge to start picking up rocks. These rocks were the tipping point. ) No one I asked seemed to be able to positively identify them. At the time, or since! While Mookaite is tempting, mostly because I got mine on Ko Mook, I think Radiolarite is it ! ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [January 18, 2015, 3:08pm UTC](https://boards.straightdope.com/t/whats-up-with-this-rock/710140/20 "2015-01-18T15:08:48Z")
> [@Mr.Miskatonic](#): > > Lots of sandpaper. > > And maybe a Dremel. After 20 minutes sanding a patch down with 240 grit wet sandpaper, I’m not sure it will take a polish, but it’s smoother now. Surprisingly the darker parts seem to sand easier, or at least the sludge from wet sanding picks up a vivid mauve colour very quickly. [Next page](https://boards.straightdope.com/t/whats-up-with-this-rock/710140.md?page=2)