Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: AndrewJ on 16/02/2008 20:52:30
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I found this rock while doing yard work about 3 years ago at my grandmothers house, it was found underneath an embankment by a river. I brought it to my local university and they were stumped as to what it is. Ideas anyone? (sorry for bad quality, need new camera)
1.a dark green color
2.some "melted" areas where the rock is shiny ans smooth
3.various crevaces
4.a strange tan substance growing on it that is able to be scratched off to reveal the original green color.
5.about the size of my fist, heavy for it's size
Pics:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi217.photobucket.com%2Falbums%2Fcc92%2Fneocloud3819%2FIMG_1344.jpg&hash=0ebdb7385b2299f09f4bf8e5bf82ec38)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi217.photobucket.com%2Falbums%2Fcc92%2Fneocloud3819%2FIMG_1345.jpg&hash=a08ebac2917fc7665a6d3ac7dfc51153)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi217.photobucket.com%2Falbums%2Fcc92%2Fneocloud3819%2FIMG_1346.jpg&hash=14f54b79a9986088bdbc7eee9b6e4130)
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First, Andrew, thanks for joining the forum - welcome.
Second - where do you live? How hard is the green stuff? Can you scratch it with a fingernail, a iron nail or not. Are there any flat planes one the green stuff that makes regular angles that are repeatedly? If so, it is some sort of crystal.
Also, what does the tan rock seem like? is is just a crust or is it an all around the green rock?
My first impression is that it might be olivine BUT that is just an impression, not at all a certainty.
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Umm, I live in Connecicut, United States, and i cant scratch it with my fingernail, but i can with an iron one. there are some flat spots, but they dont repeat, and the tan is like a crust. Thanks alot for checking it out, its getting fruturateing looking for it on google.
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was it found anywhere near lime rock park? [^]
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Nope, in my grandmothers backyard =]
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Looks like melted glass. Does that cork have anything to do with it?
Is it metalic in any way?
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Umm no ha ha the cork is for scale, and the no its not metallic
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The Heartford Basin, which is only about 20 miles wide at its widest point and which extends north-south through the state is the only place where there are sedimentary rocks in Connecticut and even there there are basalt flows that have been folded into the sedimentary rocks. The rest of the state is either gneiss or schist (metamorphic rock types) and other igneous basalts.
So, I am going to stick with the Olivine for the moment. Our hard rock geologist is on a consulting job and I am the only other who posts regularly and I am NOT an expert on hard rocks. Bass will bee back soon so check back in a few days to see if he has any other ideas.
Jim
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thanks so much for your help jimbob, i really appreciate it!
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Is it possible to get a clear close up of the texture? (both the rock and the tan stuff if possible)
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Welcome to the forum!
Looks like it may contain quartz fragments?
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Like fretback, I would love to see a clearer image. Olivene is a definite possiblility, but large masses of olivene like this are rare- usually restricted to ultramafic rocks. Other green possibilities are hornblende/augite (amphibole family) or any number of calc-silicate (skarn) rocks.
Does this green scratch easily with a knife? You meantioned it seemed heavy, how does it compare to similar sized "garden variety" rocks- twice as heavy? a bit heavier?
Can you do a streak test? (sorry, Neil, this doesn't involve running naked through a futball match- don't want to get ewe all excited) Scratch the green on some rough porcelain- what color streak does it leave?
Any micaceous minerals?
When it breaks, does it leave straight, smooth surfaces, or does it break in curved (conchoidal) surfaces like glass? Are there any minerals in the crevices?
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Sorry for late reply, havent been around all day. The rock is scratched easily with a knife, and is about twice as heavy as a normal rock of the same size. It does not break like glass, more of a smooth surface, i dont have any rough porcelain on me at the moment but i will get back to you on that. And to answer your question on the minerals, there were some debris in the crevaces, but no other form of rock. The quarts i have no clue about (not experienced)
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AndrewJ, are the white white areas that I circled harder or softer than a knife?
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Bass,
Look at the map at http://www.wesleyan.edu/ctgeology/images/CtGeoMap_big.jpg There could be a lot of ultra-mafic basalts in the Hartford Basin. These are rift faulting related basalts with dolerite. I did consider amphiboles and still do. It looks to me like something injected into sedimentary rocks. That is why I was going with the olivine since it will scratch with a iron nail. Even amphibloles, except for stuff like talc are not often found in large chunks like this, are they?
How was your trip? - PM or email OK. Also see advertising section of Oil and Gas Journal for this week, 2/17/08.
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Our hard rock geologist is on a consulting job...
Does he have anything to do with Metallic Ore? (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fbestsmileys.com%2Flol%2F16.gif&hash=c1dc69d9ae62875e79ea5868a8cfa84b)
(think about it)
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Our hard rock geologist is on a consulting job...
Does he have anything to do with Metallic Ore? (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fbestsmileys.com%2Flol%2F16.gif&hash=c1dc69d9ae62875e79ea5868a8cfa84b)
(think about it)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.mysmiley.net%2Fimgs%2Fsmile%2Fsick%2Fsick0012.gif&hash=7f79265f884a077e5279437dfc637a68) (http://www.ladies-shoes.biz/ladies-shoes/63889-1.html)
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AndrewJ, where in CT did you find this (where does your grandmother live)?
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Umm, my grandmother lives in a rural part of Connecticut called Sterling, not many people know where it is.
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The Preston Gabbro (ultramafic rocks containing dunites and pyroxenites) is somewhat south of Sterling (I think the local Indian tribe built a casino on it). Has been explored for copper, nickel and platinum over the years.
Any chance you could send me the specimen (or a piece of it)? Would love to have a look at it and then send it back. Will email my address.
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the brown rock on the outside is probably just some kind of silicate . . . the look says it's jade, and had it been found anywhere else I would probably say that. but connecticuit? I doubt it. also, definitely not turquoise. it's a tricky specimen . . . I almost feel guilty asking this of you, but have you tried certain acids on it? Hydrochloric Acid, perhaps?
If the brown part starts fizzing real sharp on contact with the acid, the crust has magnesium in it. The rock itself won't do anything, most stones are just silicon dioxide (sand/natural glass)
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I highly doubt that it's basalt, but no idea about the amphiboles.
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"If the brown part starts fizzing real sharp on contact with the acid, the crust has magnesium in it."
What?
Limestone fizzes nicely with acid, and doesn't have any Mg in it.
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Obviously, Prof., you don't know much about geochemistry. Ultramafic rocks, such as those in CT can form olivine easily. The eastern part of CT where the specimen was found contains dunites and gabbros - rocks that were formed from ultramafic intrusive igneous rocks, in which the mineral differentiation has a long time to take place as the intrusive rock cools over time.
If the Browm matric fizzes in HCL it is most likely the presence of a carbonate - something I do not even consider in this case. Mg has no such properties.
The rock itself won't do anything, most stones are just silicon dioxide (sand/natural glass)
Absolutely wrong. There is an abundance of carbonates and complex silicates in the geologic sequence as well. Pure silica is not as common as you might think.
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Magnesium dissolves completely in hydrochloric acid. It forms a common salt known as Magnesium Chloride.
I've watched it happen.
But I have another theory. I just took out an old piece of fancy jasper, and while it is slightly darker than your specimen, it has the same quartz-like areas and greenish tinge.
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and after a breif google image search, I'm going to guess it's not olivine.
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Magnesium is never found in it's elemental form in rocks as the element reacts with water at room temperature, just as elemental calcium does. No magnesium ore is disolvable by HCl. The highly reactive nature of magnesium prevents this as the bonds it forms with other elements are very stable.
For a magnesium mineral the standard test for magnesium is not using an acid. A suspected mineral which will not melt is heated to a high temperature then cooled. It is then wet with a solution of Co(NO3)2 and reheated. If magnesium is present, the mineral will turn pink to flesh-colored. This can be done in th field if you are prospecting for magnesium but you need to bring along a portable lab with blow torch.
This is in the opinion of both of the geologist present in the discussion, one a mining consultant, that it could but may not necessarily be olivine. The mechanism which put it in this area of CT are two. It came from the native rocks that are there or as a part of glacial transport from the Greenville mineral province in western CT, New York, Mass., or a similar place.
The whitish areas are also probably a closely related ultramafic mineral, a part of the ultramafic mineral solid phase diagram found at http://en.wikipedia.org/wiki/Ultramafic .
This isn't a guessing game. Bass will be able to tell what it is right off the bat when he gets the sample, if it was sent. He left on a job just after the exchange about mailing a sample. Until then, trust the pros - it quite well could be olivine or an amphibole (clino- or ortho-pyroxine.)
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Dolomite, a mixed calcium/magnesium carbonate dissolves just fine in HCl. Dolomite is one magnesium ore, another is the MgCl2 that is present in sea water. Since this is soluble in water it also dissolves in dilute HCl.
A lot of magnesium compounds are a bit too rare to use as ores, but here's what wiki has to say about a bunch of them.
"The most common magnesium carbonate forms are the anhydrous salt called magnesite (MgCO3) and the di, tri, and pentahydrates known as barringtonite (MgCO3·2H2O), nesquehonite (MgCO3·3H2O), and lansfordite (MgCO3·5H2O), respectively. Some basic forms such as artinite (MgCO3·Mg(OH)2·3H2O), hydromagnestite (4MgCO3·Mg(OH)2·4H2O), and dypingite (4MgCO3· Mg(OH)2·5H2O) also occur as minerals. Magnesite consists of white trigonal crystals. The anhydrous salt is practically insoluble in water, acetone, and ammonia. All forms of magnesium carbonate react in acids. Magnesium carbonate crystallizes in the calcite structure wherein Mg2+ is surrounded by six oxygen atoms. The dihydrate has a triclinic structure, while the trihydrate has a monoclinic structure."
An example of an even more reactive element than magnesium is sodium. Almost all the sodium compounds (as well as the metal) are obtained from salt. This too is soluble in water and in dilute HCl. The idea that high bond strength precludes solubility isn't true.
I may not be a geologist, but I do know some chemistry.
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Actually, the way we differentiate between limestone and dolomite in the field is the fizz it produces. Dolomite, as the bonding strength is high for the magnesium, is very slow to fizz with HCl while limestone, pure calcium carbonate, will practically dissolve in your hand with a very vigorous fizz. The more Mg, the less fizz. I have a sample of dolomite that will hardly fizz at all. Had I not found it in situ, I would have thought it to be marble, not dolomite.
But back to the rock in question. I should have said that magnesium silicates will not dissolve in HCl acid.
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No magnesium ore is disolvable by HCl.
I didn't say magnesium ORE. Haven't you ever gotten a fresh roll of magnesium from the hardware store? It fizzes like crazy.
But let's just drop this side topic, Fancy Jasper is my final guess.
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"For a magnesium mineral the standard test for magnesium is not using an acid."
"Actually, the way we differentiate between limestone and dolomite in the field is the fizz it produces. Dolomite, as the bonding strength is high for the magnesium, is very slow to fizz with HCl "
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see, this is why you're a bored chemist and I'm a wanna-be professor. you're bored because you have all the answers, and I say this only after searching and confirming what you said, and I still want to learn.
no sarcasm, I just learned what you said today.
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But let's just drop this side topic, Fancy Jasper is my final guess.
Jasper doesn't scratch with a knife. Haven't heard whether or not AndrewJ is sending all or part of the specimen. Will let you know if it arrives.
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well then I don't know what it is. it looks a helluvalot like fancy jasper, but I never bothered to check if fancy jasper scratches because my sample is very valuable me.
but I still doubt it's olivine.
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With all of the information by geological scientist and others that you have been given, WHY? It just doesn't make sense to me, especially since mineralogy is something you have never studied and you have admitted to only guessing.
Again WHY?
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on the contrary, I did not admit to not having studied mineralogy. I simply said that I never tested fancy jasper for its softness, or lack thereof.
over the last eight years (yes, since I was six) I have been collecting rocks and gems of different sizes and colors ranging from rock crystal to bronzite. at one point I had a good thousand or so stones, each labeled and 99% of them individual from the rest of the collection.
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But why do you say it isn't olivine? That is what I want to know.
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was it found anywhere near lime rock park?
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It was found under a creek bank near Sterling, CT. I have no idea where Lime Rock Park is located. Help me out here.
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(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fz.about.com%2Fd%2Fchemistry%2F1%2F7%2Fb%2FU%2Folivine.jpg&hash=4013490ef9f824ac74744ff2d9a027ed)\
Jimbob's sample is much too dark to be olivine.
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First it isn't my sample. Secondly, in the definition of olivine, at the same place you got the picture, http://en.wikipedia.org/wiki/Olivine, it states "Olivine is usually named for its typically olive-green color (thought to be a result of traces of nickel), though it may alter to a reddish color from the oxidation of iron." The darked, non-transparent color is the norm. Olive-green is not translucent.
This picture is of an ultramafic olivine basalt.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi38.photobucket.com%2Falbums%2Fe111%2Fgeezer69%2FOlivineBasaltCU650.jpg&hash=d84ed511d7c9a89891c1d5f475eba050)
ALL of the green minerals are olivine, even the darkest that are apparently black. The dark gray rock is the basaltic matix the olivine formed in.
The reason for the darker color of the olivine can be seen in the following diagram.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi38.photobucket.com%2Falbums%2Fe111%2Fgeezer69%2Folivine1.jpg&hash=146881f973a333366f01be95ba41e48d)
This diagram shows the end points of the olivine-amphibole-ortho- and clino-pyoxine composition. The picture you posted is the end point of the olivine composition - gem quality olivine or perididote.. (see http://en.wikipedia.org/wiki/Peridot) It falls on the top of the apex of the triangular diagram of the composition diagram. However, you can see that ALL of the area in green on the diagram is the variation that occurs in olivine composition. 99% of olivine is not like the picture of gem quality olivine you posted. The color of your olivine is very rare. It must be rare. If it were not, peridote would not be a gem mineral.
Please note that in middle of the bottom part of the diagram triangle bears the label of "olivine websterite." Thus, even these rocks of the much different chemical composition are also considered olivine.
I hope this puts to rest you delusion that it cannot possible be olivine. It could be other minerals but all are include within composition range of the triangular diagram.
You say you want to learn. All of the facts I haven presented have been presented above and had you studied this, you would have seen this already. It just seems argumentative. I will not argue. This is the last time I will post replies of substance to your inaccurate posts. I will simply say "that is not true." I have fully explained the SOUND geochemical reasons this sample is within the chemical composition of this solid phase diagram and there is no other evidence needed to prove the point.
I COULD VERY WELL BE OLIVINE
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hah? okay, I'll take your word for it.
I never really dealt with olivine much, as you can tell.
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I always got into the metallic rocks such as pyrite and peacock ore.
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I'm going to say i don't think its olivine... i have never heard of olivine crystals being of that size... i was under the impression that olivine is common in basic rocks, especially basalt and i'd be surprised if an olivine crystal of that size would form, it would take a great amount of time at considerable depth and pressure in order for such a crystel to grow to that size. I didnt realise Jasper could be green, i've only ever seen red samples and they didnt look particularly crystalline.
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that, too. I think I may have seen that fact when I was looking for a picture of it.
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btw AndrewJ, are there any rough spots that seem crystal-like? in the photo, the sample looks too smoothe to be olivine, as olivine mainly forms in rough, crystal-like bunches, and as exodus said, not in such large samples.
I have a rather large sample of rock crystal that isn't that big.
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I didnt realise Jasper could be green
Google "fancy jasper" and check the images results.
yes, most commonly it is beige or red, but fancy jasper is a dark aquamarine color.
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Hi Exodus, welcome back!
The fusion of olivine, amphiboles and clino- & orthopyroxines in the lower grade metamorphic provinces within the larger Grenville Province in North America is known to produce such stones as the one originally posted. I do not believe the green is all one crystal. It is possibly composed of small crystals of olivine, amphiboles and pyroxines.
The brownish stuff is possibly composed of iron rich alteration products of the minerals contained withing the solid phase diagram in my last post.
"there are some flat spots, but they don't repeat, and the tan is like a crust." - "4. a strange tan substance growing on it that is able to be scratched off to reveal the original green color." AND "The rock is scratched easily with a knife, and is about twice as heavy as a normal rock of the same size. It does not break like glass, more of a smooth surface,..." (from first few posts describing the rock) The fact that the cleavage is flat indicates a stable crystalline structure. The color variation indicate different crystals, smoothed by transport within a glacier or a watery environment.
I am not say it IS olivine, I am saying it could be.
Onto the web to get examples.
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AHHH im so sorry guys, ive been grounded from the computer for like a month. Umm i cant send a sample, my mom won't let me, as you might have guessed i am only a kid of 14 so i dont have as many of the responsibilities as adults =/. I will read the post later and get back to you on the questions, i can't believe this has gotten so in depth.
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Hi Andrew,
Glad you are out of the black hole and ready to resume your life. Just don't mess up again but then that is useless to tell you - I continued to get in trouble until I was senior in high school.
Anyway - when Bass gets back next week I think he may be able to help you do your own tests to figure out what this rock really is. If not, he can get you close. As I said before I am not a real hard rock guy so he is your best bet - unless Exodus has any suggestions. He is a British geology and spends more time in the pub than we American geologist so he may not be reliable. [;)]
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Andrew
I'm hare today and gnome tomorrow.
Sorry you can't send a small bit of the specimen. Will be back wednesday to try tohelp you solve this problem.
in the meantime-
you said you could scratch the specimen with a knife. Is it easy to scratch, or do you have to press down harder? If it's easy to scratch, try scratching it with a stiff piece of copper wire (not steel wire). Any luck?
Over a piece of paper, scrape the green mineral with a knife or nail until you get a bit of powder. What color is the powder? Probably white, but maybe not?
Ask your science teacher at school to put a few drops of dilute HCl (hydrochloric acid) on the specimen. Does it bubble? if not, scratch it with a nail a little, then try a couple of more drops where you scratched it. Did it bubble?
If there are places where the specimen has broken, do you see any flat, shiny surfaces? or is it just irregular? If there are flat surfaces, how large are they? When you rotate the specimen in the light, does it ever seem to catch the light and shine a bit more at one particular angle, or is it pretty much the same all over?
Can you get a friend or science teacher at your school to take a better digital picture?
Do you see any small crystals in specimen, or does it all look the same?
Are there any obvious minerals besides the green mineral? Mica? Quartz?
How heavy is this compared to a regular rock the same size? Twice as heavy?
Post your answers, and I'll take a look when I get back, or JimBob or Exodua may be able to help with all this information. Based on your answers, I may have some other tests you can try.
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shape suggests garnet...
Garnets are soft, come in a variety of colors, right size too.
Rare green ones like this are valuable....
I bet you have a garnet...
It could be ?---
http://www.toledotel.com/~ope/salepics/FMIndexA/lithicID.htm#submit1 (http://www.toledotel.com/~ope/salepics/FMIndexA/lithicID.htm#submit1)
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Garnets are soft, .....
I don't think so. Garnets are almost equal to or equal (or greater) in hardness to quartz.
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Garnets are soft, .....
I don't think so. Garnets are almost equal to or equal (or greater) in hardness to quartz.
Not only are they hard, but they have one of the highest crystallization forces of any mineral, which is why garnets are so commonly found as dodecahedral crystals
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And used as abrasives as well.
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I also live and work in Connecticut. What this rock sample looks like to me is a piece of greenish slag from one of the many old iron foundries present here during the latter 1700's. So much iron ore was mined and smelted in Connecticut that the entire state was deforested and the iron industry gave rise to famous place names such as Valley Forge.
All along the river banks of the NW and NE part of the state can be found these green/tan multicolored slag rocks or floats. I have found mountains of overgrown slag while wandering through the woods in old mining areas. I have quite a collection of similar stones and the one in the pictures. The iron smelters and foundries were always built near running water for power purposes.
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Well, it's been 4 years since I posted this, and reading back on my comments is quite amusing. I still have the rock mentioned in the original post, and it's still a mystery to me. I've looked up different images of iron slag, and it seems far too colorful and naturally crystalline to be anything like that.
Here's another picture, if anyone is still interested:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2F26.media.tumblr.com%2Ftumblr_lz6u76lPcl1qg0hobo1_500.jpg&hash=550b95e034f6f04e90f6c1f7f4a60442)
It doesn't really do the color much justice due to the lighting, but the original pictures are close enough.
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Possibly Beryl- lots of pegmatites in that part of the country. Can you scratch the green mineral with an knife?