# What kind of rock is this? **URL:** \ **Category:** Factual Questions\ **Created:** [February 20, 2016, 10:56pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648 "2016-02-20T22:56:42Z")\ **Posts on this page:** 20\ **Page:** 1
**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:** [February 20, 2016, 10:56pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/1 "2016-02-20T22:56:42Z")
I found this chunk in northern Montana back in about 2009. It appears quartz-like, is gray-green in color, measures about 2"x3". Blurry photos follow: [Photo 1](https://www.flickr.com/photos/43200610@N07/25156480915/in/dateposted-public/) [Photo 2](https://www.flickr.com/photos/43200610@N07/25063214751/in/dateposted-public/) ---
**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:** [February 20, 2016, 11:04pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/2 "2016-02-20T23:04:11Z")
[Still blurry, but wet.](https://www.flickr.com/photos/43200610@N07/25130287826/in/dateposted-public/) ---
**Author:** ![Zeldar](https://avatars.discourse-cdn.com/v4/letter/z/b77776/32.png) [@Zeldar](https://boards.straightdope.com/u/Zeldar)\ **Post date:** [February 20, 2016, 11:05pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/3 "2016-02-20T23:05:22Z")
Don’t rule out the possibility of [Coprolite](https://en.wikipedia.org/wiki/Coprolite) ---
**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:** [February 20, 2016, 11:15pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/4 "2016-02-20T23:15:11Z")
> [@Zeldar](#): > > Don’t rule out the possibility of [Coprolite](https://en.wikipedia.org/wiki/Coprolite) Thanks, but I’m looking for serious answers. ---
**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:** [February 20, 2016, 11:21pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/5 "2016-02-20T23:21:08Z")
Is there a reason why non-blurry pictures can’t be posted? ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [February 20, 2016, 11:26pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/6 "2016-02-20T23:26:09Z")
Way too blurry. You’re getting good clear images of the bench. Try holding down the shutter button half way to lock the focus, then physically move the camera away from the specimen by about the same height as the specimen. The far corner of photo 2 that is almost in focus. From that my best guess would be quartzite. But we really need in focus photos so we can determine grain size and structure. ---
**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:** [February 20, 2016, 11:32pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/7 "2016-02-20T23:32:17Z")
> [@Blake](#): > > Way too blurry. You’re getting good clear images of the bench. Try holding down the shutter button half way to lock the focus, then physically move the camera away from the specimen by about the same height as the specimen. > > The far corner of photo 2 that is almost in focus. From that my best guess would be quartzite. > > But we really need in focus photos so we can determine grain size and structure. I’ll give it another shot. Thought I had it on macro. ---
**Author:** ![Zeldar](https://avatars.discourse-cdn.com/v4/letter/z/b77776/32.png) [@Zeldar](https://boards.straightdope.com/u/Zeldar)\ **Post date:** [February 20, 2016, 11:38pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/8 "2016-02-20T23:38:03Z")
> [@Zeldar](#): > > Don’t rule out the possibility of [Coprolite](https://en.wikipedia.org/wiki/Coprolite) > [@Chefguy](#): > > Thanks, but I’m looking for serious answers. As a shot at a serious answer, compare some of the images [here.](https://images.search.yahoo.com/search/images;_ylt=AwrBTzxY.chWYy8A3_5XNyoA;_ylu=X3oDMTB0N2Noc21lBGNvbG8DYmYxBHBvcwMxBHZ0aWQDBHNlYwNwaXZz?p=coprolite&fr=yfp-t-201&fr2=piv-web) ---
**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:** [February 20, 2016, 11:39pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/9 "2016-02-20T23:39:52Z")
Okay, let’s try these (wetted to bring out the texture/color): [One](https://www.flickr.com/photos/43200610@N07/25063886161/in/dateposted-public/) [Two](https://www.flickr.com/photos/43200610@N07/25130784486/in/dateposted-public/) [Three](https://www.flickr.com/photos/43200610@N07/25063856101/in/dateposted-public/) ---
**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:** [February 20, 2016, 11:41pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/10 "2016-02-20T23:41:57Z")
> [@Zeldar](#): > > As a shot at a serious answer, compare some of the images [here.](https://images.search.yahoo.com/search/images;_ylt=AwrBTzxY.chWYy8A3_5XNyoA;_ylu=X3oDMTB0N2Noc21lBGNvbG8DYmYxBHBvcwMxBHZ0aWQDBHNlYwNwaXZz?p=coprolite&fr=yfp-t-201&fr2=piv-web) It really looks nothing like those, although you likely couldn’t tell by the original photos. ---
**Author:** ![Ignotus](https://avatars.discourse-cdn.com/v4/letter/i/ecc23a/32.png) [@Ignotus](https://boards.straightdope.com/u/Ignotus)\ **Post date:** [February 20, 2016, 11:50pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/11 "2016-02-20T23:50:06Z")
It looks indeed a lot like quartz, maybe with some inclusions of mica. Can you estimate the hardness? Does it scratch glass? ---
**Author:** ![Ionizer](https://avatars.discourse-cdn.com/v4/letter/i/5daacb/32.png) [@Ionizer](https://boards.straightdope.com/u/Ionizer)\ **Post date:** [February 20, 2016, 11:55pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/12 "2016-02-20T23:55:57Z")
My bet is that it is [smoky quartz](https://www.google.com/search?q=smoky+quartz&safe=off&biw=819&bih=493&source=lnms&tbm=isch&sa=X&sqi=2&ved=0ahUKEwjao6X_w4fLAhXH2SYKHWtVAoEQ_AUIBigB) - which is a somewhat commonly found mineral in Montana (at least according to a number of quick googlings of ‘Montana quartz’, fwiw). As a kid, I collected all types of quartz’s, and that looks quite like one of my favorites (the smoky variety, that is). ETA - that above link: if you click on the ‘rough’ section for pics at top of page, its much easier to see the comparability ---
**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:** [February 20, 2016, 11:59pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/13 "2016-02-20T23:59:04Z")
> [@Ignotus](#): > > It looks indeed a lot like quartz, maybe with some inclusions of mica. Can you estimate the hardness? Does it scratch glass? I don’t have any glass around that I want to try it on, unfortunately. I have a couple of smaller pieces that I’m pretty sure are quartz; one is a nice yellow color with a bit of red on one end; the other is a very pretty green. None of the three is a color that I’ve associated with quartz in the past, but then I’m not a rockhound. ---
**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:** [February 21, 2016, 12:03am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/14 "2016-02-21T00:03:33Z")
> [@Ionizer](#): > > My bet is that it is [smoky quartz](https://www.google.com/search?q=smoky+quartz&safe=off&biw=819&bih=493&source=lnms&tbm=isch&sa=X&sqi=2&ved=0ahUKEwjao6X_w4fLAhXH2SYKHWtVAoEQ_AUIBigB) - which is a somewhat commonly found mineral in Montana (at least according to a number of quick googlings of ‘Montana quartz’, fwiw). As a kid, I collected all types of quartz’s, and that looks quite like one of my favorites (the smoky variety, that is). > > ETA - that above link: if you click on the ‘rough’ section for pics at top of page, its much easier to see the comparability I think you may have nailed it. Some of those look very much like it. I found mine up along the Dinosaur Trail in the town of Malta. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [February 21, 2016, 12:20am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/15 "2016-02-21T00:20:14Z")
Can we get a dry non-blurry picture? I don’t think it’s smokey quartz, since it looks like your rock is bits of white/translucent quartz on a darker rock, not dark-colored quartz. I think more likely it’s a part of a quartz-rich intrusion into another rock type. My somewhat-informed guess based on the local geology is that the non-quartz stuff is probably some sort of limestone or dolemite, although that part of Montana also has tons of glacial erratics so it could be some exotic thing brought down from Canada with the ice sheets. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [February 21, 2016, 3:02am UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/16 "2016-02-21T03:02:48Z")
I’m gonna say feldspar. First of all, most of the earth’s crust is feldspar so it’s an easy guess. But on top of that it’s not uniform, the black stuff appears to be inclusions in the quartz-like material. That’s what many feldspars will look like after erosion. Or just plain quartz with some black inclusions. ---
**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:** [February 21, 2016, 2:50pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/17 "2016-02-21T14:50:08Z")
I’ll try to get a better-lighted dry shot this morning sometime, but thanks for the help so far. ---
**Author:** ![Spectre\_of\_Pithecanthropus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spectre_of_pithecanthropus/32/12343_2.png) [@Spectre\_of\_Pithecanthropus](https://boards.straightdope.com/u/Spectre_of_Pithecanthropus)\ **Post date:** [February 21, 2016, 3:13pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/18 "2016-02-21T15:13:01Z")
> [@TriPolar](#): > > I’m gonna say feldspar. First of all, most of the earth’s crust is feldspar so it’s an easy guess. But on top of that it’s not uniform, the black stuff appears to be inclusions in the quartz-like material. That’s what many feldspars will look like after erosion. Or just plain quartz with some black inclusions. Would feldspar have that rough glassy fracture pattern? At least, I assume it was fractured. ---
**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:** [February 21, 2016, 5:52pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/19 "2016-02-21T17:52:01Z")
Okay, last shot at getting good shots. It’s remarkably difficult to photograph. All the surfaces have a glassy shine to them (some look bubbled, some rippled, another is more faceted), which doesn’t come out well in photos. I suppose it could be some sort of other mineral that was somehow encapsulated in quartz. Bright light only seems to penetrate through one area. Anyway, three of these were taken in natural light, the last one under a CFL, which probably mucks up the colors. [One](https://www.flickr.com/photos/43200610@N07/25080641041/in/dateposted-public/) [Two](https://www.flickr.com/photos/43200610@N07/25080641041/in/dateposted-public/) [Three](https://www.flickr.com/photos/43200610@N07/24547116563/in/dateposted-public/) [Four](https://www.flickr.com/photos/43200610@N07/25080730611/in/dateposted-public/) ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [February 21, 2016, 7:04pm UTC](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648/20 "2016-02-21T19:04:02Z")
> [@Spectre\_of\_Pithecanthropus](#): > > Would feldspar have that rough glassy fracture pattern? At least, I assume it was fractured. It can look like that. The classic images of feldspar will show crystalline shapes that are apparent on the surface as it’s found in the ground. But after weathering it can take that kind of appearance. But so can a lot of rocks. Rock hounds would break open a piece like that to get a better look at the insides that haven’t been exposed to the weather. It could be some simple igneous formation of quartz and other minerals. Checking it under a black light or testing it with some acid might reveal more clues. It’s very difficult to positively identify any rock with just a photo. [Next page](https://boards.straightdope.com/t/what-kind-of-rock-is-this/746648.md?page=2)