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How to identify a metal ? Answered

Hi ! Into a terrain near a very old volcano and a river, my brother found fragments of obsidian of various sizes and colors. Some of them are "glued" to metallic stones, and some others contain marbles of metals ... He also found a heavy metallic rocks (encrusted with obsidian) who reacts with magnet, and an other light one (without obsidian) who does not react with magnet. Do you know a mean to identify those metals ? (I Googled but found nothing very useful so far) Or do you have a clue of what it could be ? #1 is a metallic rock encrusted with obsidian. It must be iron because it's heavy, the rust is red, and it reacts to magnet. #2 and #3 is obsidian with marble of metal who reacts to magnet. #4 is an unknown (metallic ?) rock. It is light (150 grams for 200 cm3 - 0.33 pounds for 12 cubic inches), of the color of silicon (or the graphite of paper pen !), does not react to magnet but is (electric) conductor with resistance near 0 ohm.


This may just be ignorant, but could you use one of the DIY spectroscopes on the site for identifying elements in the rocks?

. hmmmm I tried searching for spectroscope/spectrescope/spectrascope/spectriscope and didn't find anything.

. Thanks. I found this (putting spectra in quotes in the title threw me off, it was in the 'scope hits), but it's only for visible light. Not sure that will work in this case (though it might give some valuable hints).

Oh, you know I think I was confusing spectrometer with spectroscope.

I'm not sure, but I think spectroscopy only apply to gas ... :o/ I remember few month ago, I've read an article where it explained spectroscopy. If I recall correctly, there are two methods : 1) you heat the gas sample and you analyze the light emitted by the sample ( you'll get a "positive" spectrum : emission spectrum ). 2) you light the gas sample with a white light and you analyze the light filtered by the sample ( you'll get a "negative" spectrum : absorption spectrum ).

. Since you weren't sure, I did a Q&D search on spectroscopy and found "The branch of physics concerned with the production, measurement, and interpretation of electromagnetic spectra arising from either emission or absorption of radiant energy by various substances." - Cotton, Inc. (my emphasis)

Though "various" does not mean all ... :o/ Because, for gas and transparent liquids or solids, I imagine it's possible to get the absorption spectrum by using this gas or this transparent liquid or liquid as a filter. But for opaque substances, the only mean (with spectroscopy in the domain of the visible light) would be to analyze the "reflected" light ... but will it work correctly with tiny and "non flat" samples ? :o/ As soon as I'll have made a spectrophotometer or a monochromator, I will try anyway :o)

. That was just a representative sample. I looked at 5-6 defs and none specified the state of the material. . I didn't spend much time reading, but from what I gathered there are three types of spectrography: stimulated emission (bombard it with energy, eg, x-rays), absorption (pass a light (not necessarily visible) of known spectra (spectrum?) through the material), and reflective (not sure, but I'll bet it means what it says; might involve polarization). . Now that I think about it, when I was in school, we had a device that was shaped like a small telescope with a flare on one end. If you pointed the flared end toward a light and looked in the other end, you would see the spectrum. No power was required. Maybe you could stick something like that on the front of a camera and use the images to to do some analysis. . > monochromator . I learned a new word!

. I called a friend, who had studied Petroleum Geology in college, but he doesn't remember enough to say anything about your obsidian with any certainty. He said he'll come over and take a look at your pics, but he doesn't have high hopes he will be able to tell us anything (it's been 30 years since he was in college). :( . You may be able to look up the volcano and find some info on what the magma contains. This should at least narrow down your choices.

Oh, thanks a lot NachoMahma. :-)

. You may be able to look up the volcano and find some info on what the magma contains. This should at least narrow down your choices.

Actually, there few informations available on the net. Most are quick overview. And I can't move to the library of the nearest city (locked at home because of my back ...) to try to find more info ... :o/

This volcano is just a little one of a chain of about 60 km (37 miles) long.
The oldest volcano are north, in a zone where there was the sea. The most recent (700,000 years old) volcano are south.
The main rock they extract (in the southern part of this chain) is basalt.
They say nothing about obsidian ... :o/

There is a great variety of minerals and ore in this 60km square area.
There is even a prehistorical mine of copper ...

. Well, my friend came by and looked at the pics, but it's just been to long since he's studied Geology. He has "no idea." :( . Where is the volcano? I'll guess that volcanoes in the same chain would have similar compositions.

from what I remember, obsidian is mostly silicon.

Yes. Silicon dioxide, like quartz and glass. It's a magma who did not "crystallized" because it was cooled too quickly.

. Well, my friend came by and looked at the pics, but it's just been to long since he's studied Geology. He has "no idea." :(

Never mind. It's not "vital" ...
Tell him "thank you" from me =o)

. Where is the volcano? I'll guess that volcanoes in the same chain would have similar compositions.

Probably. But once at the surface, the magma could have mixed with different kind of minerals. :o/
The northern soils of the chain is red.
The southern soils of the chain are mainly white clays.

Here is a map I've found (just to give an idea of the area).
I translated it and I added some more info gathered from other sites.

The red circle is where my bro found those samples.
The volcanic zone (brown) just at the south of this circle is where they extract basalt.


#4 conducts without resistance? At room temperature?

Quick, sell it - a room-temperature superconductor is worth millions!

Since they all came off the same volcano, they're all likely to contain different proportions of the same substances. I would hazard a guess that #4 is magnetic, but your magnet is weak (or so heavy that the effort of lifting the magnet masks the effort required to pull it off the rock).

I would wave rock #4 around a compass on a firm base and watch the compass - does it twitch?

I meant "with a very low resistance" of course ;oP

About #4 :

It's like an aggregate of metallic grains.

As I don't have a compass, I scratched the stone and I put a magnet over the sand. It attracted some grains ...
I think this stone contains less than 5% of magnetic metal.

When I scratched the stone, I noticed a very very light and thin dark dust. It was like a smoke, but it fallen down after a 5 centimetres "flight" (hope it's not toxic ... I sleep in the same room !!)

I watched the grains with a microscope.
There are some tiny crystal grains (I'd say less than 15%), and all the rest is grains of an unknown non magnetic metal (more than 80%).

It does not look aluminium (unless it's native aluminium ?)

I could try to measure the density of this metal thanks to the Archimedes' principle and compare it with various pure metals, but sorting the grains appears like a very long and boring task ... I hope there is an other mean ... =o)

Here are two pictures took with the webcam of the microscope ...


Galena , containing both lead and silver, used in crystal radios, is very conductive. The crystals are square and break into square pieces.

I do have two samples of galena in my collection. It does not look galena. My crystals of galena are large compared to the grains of #4. Also, #4 is very light compared to galena. Actually, I'm wondering if #4 does not contain a great amount of carbon ...

From my end, I have a hard time telling with just pictures. If I feel the rock/mineral and see it (sometimes smell helps too, especially in the case of sulfur ores, etc. Some things are misleading by sight alone (well noted are the golden colored pyrites containing iron, and not gold).

Yes, I understand how difficult it may be ... =o)

Don't know if this may help :
The approximate volume of #4 stone, is 200 cm3 (12 cubic inch).
And its weight is 150 grams ( 0.33 pounds).

Maybe it's not volcanic (as there is a river near the place where my bro found it).
It could be a kind of graphite mixed with clay and iron oxide ... I will try to burn it =o)

Even without any iron, if I remember correctly, graphite is a fairly good conductor. I remember making temporary little "traces" with a pencil on paper, and then showing how it conducts electricity

Note : seems aluminium does not exist pure in the nature. It's mainly aluminium oxide, and the main ore is bauxite ... So I guess this is not aluminium.

No, you never get native aluminium, not even from a lightning strike - the metal is just too reactive.

There's no point in checking the density, since you probably have a mixture of rock, not metals.

Iron oxide can hold a significant magnetic field, even though it's not a pure metal. That's how audio and video cassette tape works - the brown colour is magnetic iron oxide. In it's natural, lumpy state, it is often called lode stone.

Aluminium metal production and refinement

Although aluminium is the most abundant metallic element in the Earth's crust (believed to be 7.5 to 8.1 percent), it is rare in its free form(emphasis added), occurring in oxygen-deficient environments such as volcanic mud, and it was once considered a precious metal more valuable than gold. Napoleon III, emperor of the French, is reputed to have given a banquet where the most honoured guests were given aluminium utensils, while the other guests had to make do with gold ones.[13][14]wikepedia

I could put some sample of it into an acid, and if I see some bubble appears, that may gives some more indications =oP

Aluminum is very rare-if bauxite ore is hit with a lightning bolt you can have aluminum metal formed-but it is possible. Before mid 1800s aluminum was a precious metal-until it was discovered that electricity could refine it. You need to try a geology book or geologist (if avalible), or try some of the local rock-hounds.

. Ask a Geology teacher/professor to look at them. If they are local, he/she will probably be able to ID by sight. . Petroleum Engineers usually know a lot about rocks. One on the drilling side of the business will certainly know his/her rocks. . I've never tried it, but it sounds like trebuchet03 has a good idea. Might help to offer to exchange an hour's worth of work (or something else they think is valuable) for the service, especially if it's a $20K machine.

I doubt I'll have easily access to a Geology teacher/professor or to a Petroleum Engineers ..... :o/
I will search a french forum about geology. Maybe I'll found some specialists there.

thanks for the idea =o)

Might help to offer to exchange an hour's worth of work

Is that really so simple in USA ? =o)
Here, a single minute of work would require filling tones of forms and administrative tasks ! lol

> Is that really so simple in USA ? . It works often enough that it's worth asking. I've bartered my services (mainly computer work, but I've swept floors and even babysat) for all sorts of things. No paperwork, just a handshake.


10 years ago

Well, the only metals, IIRC, that are natuarlly magnetic are iron, cobalt, and nickel. I'm betting #1 has iron in it. #4 - It is a conductor of heat or electric current?

#4 - It is a conductor of heat or electric current?

Electric =o)

number 4 could be pretty much anything. My guess (Just my guess, I know almost nothing of rocks) is alluminum number 1 is definately a type of iron

Yeah, aluminium is the first idea that came to my mind too (as it is light).
Though, #4 is an aggregate of tiny grains. A big part of the mass of the stone is "gazeous" =o)

About #1, yeah, the red rust make me think about iron too.

Note : though, seems aluminium does not exist pure. It's mainly aluminium oxide, and the main ore is bauxite.

So it *doesn't* conduct heat well, but it conducts electricity wonderfully?

Heat one side... and then feel the other :P Its hardly scientific -- unless you know the temp. of the heat source & use a thermometer.

I think I will postpone this test as long as possible ........... =o]

Do you live near a metal scrap yard? Typically medium to large scrap yards will have an X-ray fluorescence spectrometer -- probably looks like a gun and it burns a tiny hole in the metal to identify ;) It's a cool circa 20K dollar instrument :p Maybe if you ask nicely, they'll scan it for you - IIRC, it takes a few seconds for ferrous materials, and maybe half a minute or so for Aluminum, so it's not like it will take much of their time :D

There are some "civic amenity sites" here and there, but they only collect household wastes. Final sorting and recycling is centralized somewhere else ... :o/

Thanks for this idea =o)
I'll ask to the guy of the C.A.S. next time I'll go there. Maybe he'll know where is the main recycling center.