# What kind of rock/stone was that? **URL:** \ **Category:** Factual Questions\ **Created:** [October 7, 2003, 11:24am UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032 "2003-10-07T11:24:40Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Phlosphr](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@Phlosphr](https://boards.straightdope.com/u/Phlosphr)\ **Post date:** [October 7, 2003, 2:45pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/21 "2003-10-07T14:45:11Z")
> [@](#): > > Now Phlosphr, conglomerate is definitely not metamorphic Huh?? Conglomerate means being made up of parts from various sources or of various kinds…Thats what metamorphic rock, rock that is made up of different things…Check my cite. And Pantellerite, calm down you are right! ---
**Author:** ![T.Mehr](https://avatars.discourse-cdn.com/v4/letter/t/ccd318/32.png) [@T.Mehr](https://boards.straightdope.com/u/T.Mehr)\ **Post date:** [October 7, 2003, 2:47pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/22 "2003-10-07T14:47:57Z")
granite \Gran"ite, n. [It. granito granite, adj., grainy, p. p. of granire to make grainy, fr. L. granum grain; cf. F. granit. See Grain.] (Geol.) A crystalline, granular rock, consisting of quartz, feldspar, and mica, and usually of a whitish, grayish, or flesh-red color. It differs from gneiss in not having the mica in planes, and therefore in being destitute of a schistose structure. Note: Varieties containing hornblende are common. See also the Note under Mica. Source: Webster’s Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc. ---
**Author:** ![NurseCarmen](https://avatars.discourse-cdn.com/v4/letter/n/5daacb/32.png) [@NurseCarmen](https://boards.straightdope.com/u/NurseCarmen)\ **Post date:** [October 7, 2003, 2:50pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/23 "2003-10-07T14:50:18Z")
The shale in Northern Minnesota has fun campfire qualities. If you can find the “oily shale” (this is what I grew up knowing it was called, I’m unsure if there is any oil in it) it’s fun to throw in the fire for a mini-fireworks show. But it doesn’t break apart like you describe, and no other description you gave makes me think shale. Considering it’s Northern Minnesota, I may be completely wrong about the Shale, mistaking it for [taconite.](http://www.geo.umn.edu/mgs/virt_egg/if_taconite.htm) But [Shale](http://dph1701.tripod.com/geology/geopics/shale.jpg) has some viariety to it, so it could be some form of shale. ---
**Author:** ![T.Mehr](https://avatars.discourse-cdn.com/v4/letter/t/ccd318/32.png) [@T.Mehr](https://boards.straightdope.com/u/T.Mehr)\ **Post date:** [October 7, 2003, 2:54pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/24 "2003-10-07T14:54:43Z")
\*\* Phlosphr \*\* check your cite under the section ‘Sedimentary Rocks’ to find conglomerate. It’s a sediment made up of round peices (as opposed to a breczie). ---
**Author:** ![Phlosphr](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@Phlosphr](https://boards.straightdope.com/u/Phlosphr)\ **Post date:** [October 7, 2003, 3:48pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/25 "2003-10-07T15:48:45Z")
> [@](#): > > Phlosphr > check your cite under the section ‘Sedimentary Rocks’ to find conglomerate. It’s a sediment made up of round peices (as opposed to a breczie). I understand that but I was using it outside the context of the stone world. I was using it as a descriptor not a noun. And **t.mehr** - Webster’s dictionary says: > [@](#): > > \1 : a very hard natural igneous rock formation of visibly crystalline texture formed essentially of quartz and orthoclase _ **OR** _ microcline and used especially for building and for monuments… Yes in most cases microcline does carry mica in it, however this is not the case all of the time. And this is waaay too tangental a subject for the OP. Furthermore, do you like rocks? Yes? Me too. So let’s just figure out what this stone in the OP is instead of bickering… I still think the OP’s rock is of the metamorphic family, what exactly the composition was is still a mystery…maybe the OP will go to any number of identifying sites and post a pic. ---
**Author:** ![Yossarian](https://avatars.discourse-cdn.com/v4/letter/y/9de0a6/32.png) [@Yossarian](https://boards.straightdope.com/u/Yossarian)\ **Post date:** [October 7, 2003, 4:16pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/26 "2003-10-07T16:16:54Z")
(Sorry, **Phlosphr**! I get carried away by rocks… especially felsic rocks like Granite… which are my field of study!) One last time before the OP is addressed: it does not matter what your M-W dictionary says. What matters is what the [IUGS](http://www.iugs.org) says, which is that the only essential components in granite are alkali feldspar (microcline usually), plagioclase, and quartz. Yes, many, many granites have accessory mica but the presence of mica is not necessary nor does the lack of mica preclude a rock from being called “granite”. What we need to help constrain this problem (since we lack either a sample or a picture!) is a geologic map of Alsace. This will at least tell us what it **could** be (and I think that Alsace has both igneous and sedimentary rocks, but lacks metamorphic rocks), because right now the best answer is “anything, fractured and wet”! If I make it over to the library today, I’ll see what I can find. ---
**Author:** ![Nils](https://avatars.discourse-cdn.com/v4/letter/n/d6d6ee/32.png) [@Nils](https://boards.straightdope.com/u/Nils)\ **Post date:** [October 7, 2003, 4:33pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/27 "2003-10-07T16:33:28Z")
On the outside it looks a bit like this basalt www.geo.umn.edu/mgs/virt\_egg/basalt.htm it just isn’t red and the inclusion of “my” stone are much smaller. I’m trying to find a picture of a similar stone on the net, so far unsuccessfully. If anyone knows a good site please inform me. ---
**Author:** ![Yossarian](https://avatars.discourse-cdn.com/v4/letter/y/9de0a6/32.png) [@Yossarian](https://boards.straightdope.com/u/Yossarian)\ **Post date:** [October 7, 2003, 5:41pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/28 "2003-10-07T17:41:12Z")
By “inclusions” do you mean minerals/crystals or pieces of rock? ---
**Author:** ![Yossarian](https://avatars.discourse-cdn.com/v4/letter/y/9de0a6/32.png) [@Yossarian](https://boards.straightdope.com/u/Yossarian)\ **Post date:** [October 7, 2003, 5:43pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/29 "2003-10-07T17:43:43Z")
Try looking around here: [http://geology.csupomona.edu/alert/igneous/ignrxs.htm](http://geology.csupomona.edu/alert/igneous/ignrxs.htm) and here: [http://geology.csupomona.edu/alert/metamorphic/metarxs.htm](http://geology.csupomona.edu/alert/metamorphic/metarxs.htm) ---
**Author:** ![Nils](https://avatars.discourse-cdn.com/v4/letter/n/d6d6ee/32.png) [@Nils](https://boards.straightdope.com/u/Nils)\ **Post date:** [October 7, 2003, 5:56pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/30 "2003-10-07T17:56:11Z")
The inclusion look more like little crystals. They are little areas with a smooth surface, that reflect light. But very few and \<1mm in diameter. I will look around the pages you posted, but I’m not sure my Harddisk will make it any longer (it started to make strange screaming noises half an hour ago). ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [October 7, 2003, 5:57pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/31 "2003-10-07T17:57:18Z")
> [@](#): > > \*Originally posted by Pantellerite \* > **One last time before the OP is addressed: it does not matter what your M-W dictionary says. What matters is what the [IUGS](http://www.iugs.org) says** D\*ng, I thought that was going to be a citation. Aplite is a fine-grained granite without much mica. ---
**Author:** ![Phlosphr](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@Phlosphr](https://boards.straightdope.com/u/Phlosphr)\ **Post date:** [October 7, 2003, 6:17pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/32 "2003-10-07T18:17:38Z")
Out on a limb here **Pentellerite** could it be a _metasedimentary_ rock such as a schist? That region in France apparently has a lot of schist and granites… ---
**Author:** ![Yossarian](https://avatars.discourse-cdn.com/v4/letter/y/9de0a6/32.png) [@Yossarian](https://boards.straightdope.com/u/Yossarian)\ **Post date:** [October 7, 2003, 7:37pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/33 "2003-10-07T19:37:08Z")
I couldn’t find a proper on-line site, **RM Mentock** , but for any one that’s terribly interested, here’s a real one: Streckeisen, A.L., 1973. Plutonic rocks, classification and nomenclature recommended by the IUGS Subcommission on the Systematics of Igneous Rocks: Geotimes, v. 18, n. 10, p. 26-30. **Phlosphr** , it sounds possible. If he’s seeing crystals rather than rock clasts, it’s certainly more likely to be crystalline (igneous or metamorphic) than sedimentary. However, he says “not flaky” which sounds like “not micaceous” which would seem to preclude any metasedimentary schist (in which mica minerals are extremely common!) Are you seeing the crystals in an otherwise fine grained matrix? It may be an aphanitic igneous rock. Is the entire rock coarsely crystalline (at least coarse enough to resolve every individual grain with the naked eye)? If so, do the grains have a common orientation? (Yes = possibly a foliated metamorphic rock) Or are the grains oriented randomly? (Phaneritic igneous rock or non-foliated metamorphic rock). This shit’s hard enough to do sometimes WITH a hand-sample and hand lens! ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [October 7, 2003, 10:05pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/34 "2003-10-07T22:05:08Z")
Do you have a digital camera Nils? If you can email me a photo of the rock, I’ll resize it to an easily viewable size and post a link for everyone to see. To email me click on my profile. ---
**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:** [October 7, 2003, 10:45pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/35 "2003-10-07T22:45:44Z")
Or a scanner; even plonking the flattest side on a document scanner should produce a fairly decent image. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [October 7, 2003, 10:59pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/36 "2003-10-07T22:59:21Z")
[CLASSIFICATION OF IGNEOUS ROCKS](http://geology.csupomona.edu/alert/igneous/igclass.htm), from Cal Pomona I think. Seems there is some arguments. 🙂 ---
**Author:** ![Nils](https://avatars.discourse-cdn.com/v4/letter/n/d6d6ee/32.png) [@Nils](https://boards.straightdope.com/u/Nils)\ **Post date:** [October 7, 2003, 11:09pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/37 "2003-10-07T23:09:53Z")
I haven’t got neither a scanner nor digital camera. I tried installing an old webcam but it didn’t work. Sorry. I can’t see any other fine grains except for the crystaline inclusions. I have checked several of picture databases (?). With google-picture search I found this one www.bhc.edu/academics/science/harwoodr/Geol101/Labs/Igneous/images/ign09.jpg , which comes close. “My” stone is a little bit darker and its surface structure is a bit coarser. I also remember other remnants of the stone to have those round holes you can see on the half right. The two stones I have here don’t have them, but the others had(I just remembered when I saw this picture). ---
**Author:** ![Nils](https://avatars.discourse-cdn.com/v4/letter/n/d6d6ee/32.png) [@Nils](https://boards.straightdope.com/u/Nils)\ **Post date:** [October 7, 2003, 11:17pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/38 "2003-10-07T23:17:56Z")
Oh, and the problem is, this pic is from a test to identify stones, so this doesn’t help me that much, maybe one of you “Dope-Rockers” (or Rock-Dopers?:)) isn’t as helpless as me… ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [October 8, 2003, 12:30am UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/39 "2003-10-08T00:30:27Z")
> [@](#): > > \*Originally posted by Nils \* > **the problem is, this pic is from a test to identify stones** The correct answer to [that test](http://www.bhc.edu/academics/science/harwoodr/Geol101/Labs/Igneous/Igsamp09.htm) is Porphyritic Felsic Rhyolite, according to the key. Have you seen [this one](http://www.bhc.edu/academics/science/harwoodr/Geol101/Labs/Sediment/Sed05.htm) or [this one](http://www.bhc.edu/academics/science/harwoodr/Geol101/Labs/Sediment/Sed11.htm)? ---
**Author:** ![antechinus](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@antechinus](https://boards.straightdope.com/u/antechinus)\ **Post date:** [October 8, 2003, 3:34am UTC](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032/40 "2003-10-08T03:34:28Z")
First rule of making a campfire: **Dont use river rocks** [Previous page](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032.md?page=1) [Next page](https://boards.straightdope.com/t/what-kind-of-rock-stone-was-that/206032.md?page=3)