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Author Topic: Can anyone Identify this?  (Read 40273 times)

Offline JimBob

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« Reply #25 on: 25/02/2008 02:43:05 »
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.)


« Last Edit: 25/02/2008 02:59:59 by JimBob »
 

Offline Bored chemist

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« Reply #26 on: 25/02/2008 19:46:03 »
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.
 

Offline JimBob

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« Reply #27 on: 25/02/2008 20:04:47 »
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.
« Last Edit: 26/02/2008 04:28:00 by JimBob »
 

Offline Professor Gaarder

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« Reply #28 on: 27/02/2008 01:02:55 »
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.
 

Offline Bored chemist

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« Reply #29 on: 27/02/2008 19:22:51 »
"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 "
 

Offline Professor Gaarder

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« Reply #30 on: 28/02/2008 01:13:15 »
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.
 

Offline Bass

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« Reply #31 on: 29/02/2008 19:19:54 »
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.
 

Offline Professor Gaarder

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« Reply #32 on: 01/03/2008 17:38:48 »
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.
 

Offline JimBob

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« Reply #33 on: 01/03/2008 18:02:04 »
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?
 

Offline Professor Gaarder

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« Reply #34 on: 01/03/2008 18:17:56 »
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.
 

Offline JimBob

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« Reply #35 on: 01/03/2008 18:41:24 »
But why do you say it isn't olivine? That is what I want to know.
 

Offline ok0510

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« Reply #36 on: 01/03/2008 22:58:19 »
was it found anywhere near lime rock park? 
 

Offline JimBob

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« Reply #37 on: 01/03/2008 23:18:43 »
It was found under a creek bank near Sterling, CT. I have no idea where Lime Rock Park is located. Help me out here.
 
 

Offline Professor Gaarder

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« Reply #38 on: 02/03/2008 00:20:47 »
\

Jimbob's sample is much too dark to be olivine.
 

Offline JimBob

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« Reply #39 on: 02/03/2008 01:46:03 »
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.




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.



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

 
« Last Edit: 02/03/2008 01:48:17 by JimBob »
 

Offline Professor Gaarder

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« Reply #40 on: 02/03/2008 02:38:47 »
hah? okay, I'll take your word for it.

I never really dealt with olivine much, as you can tell.
 

Offline Professor Gaarder

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« Reply #41 on: 02/03/2008 02:39:13 »
I always got into the metallic rocks such as pyrite and peacock ore.
 

Offline Exodus

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« Reply #42 on: 02/03/2008 15:21:14 »
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.
 

Offline Professor Gaarder

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« Reply #43 on: 02/03/2008 15:46:53 »
that, too. I think I may have seen that fact when I was looking for a picture of it.
 

Offline Professor Gaarder

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« Reply #44 on: 02/03/2008 15:49:48 »
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.
 

Offline Professor Gaarder

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« Reply #45 on: 02/03/2008 15:51:20 »
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.
 

Offline JimBob

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« Reply #46 on: 02/03/2008 17:27:53 »
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.
« Last Edit: 02/03/2008 18:15:38 by JimBob »
 

Offline AndrewJ

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« Reply #47 on: 07/03/2008 21:15:43 »
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.
 

Offline JimBob

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« Reply #48 on: 07/03/2008 21:51:41 »
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.  ;)
 

Offline Bass

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« Reply #49 on: 08/03/2008 05:20:36 »
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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« Reply #49 on: 08/03/2008 05:20:36 »

 

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