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Author Topic: trying to identify the metals in these rocks  (Read 1736 times)

Offline ExplorerShaun

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trying to identify the metals in these rocks
« on: 30/10/2012 18:28:26 »
These rocks were found near the summit of Mt. Illimani, in Bolivia. The area is known for gold and iron, so my guess is that is contains both. The flat rock weighs 105 grams, while the rounder rock weighs 136 grams.

Is there a way to identify all the elements without breaking down the rocks?


 

Offline CliffordK

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Re: trying to identify the metals in these rocks
« Reply #1 on: 30/10/2012 19:29:36 »
You could, of course, try to stick a magnet to the rock.  Perhaps a Neodymium (NdFeB) magnet.  That should indicate a likelihood of the presence Iron.

I would assume that most assays would be destructive.  However, X-Ray Fluorescence would be a non-destructive, and generally quantitative analytic method, but probably not suited for use at home.
 

Offline Bill S

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Re: trying to identify the metals in these rocks
« Reply #2 on: 30/10/2012 20:16:41 »
Bringing a compass close to the rock might be a sensative test for iron. 

You could try scratching various parts with a knife, file or bit of quartz to obtain a streak and assess hardness.
 

Offline ExplorerShaun

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Re: trying to identify the metals in these rocks
« Reply #3 on: 01/11/2012 16:23:41 »
Thank you for both responses! The magnet did cause a slight, negative to negative reaction with both rocks. I used a compass and it did pull on the needle. Since there are flecks of silver (could be tin or nickel?), copper and gold, I would guess that be the reasoning for such a low magnetic field.

Since the rounder one is the size of a ping-pong ball, yet weighs 136g... I would guess a heavier metal?
 

Offline Bill S

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Re: trying to identify the metals in these rocks
« Reply #4 on: 01/11/2012 20:41:15 »
Magnetite or native iron would probably be the usual suspects, but if the reaction is slight the amount is going to be small.  Pyrrhotite is another possibility, but it tends to be lighter (wieght) than the other two.

I believe the commonest form in which tin is found is cassiterite, which is usually dark brown to black.  It may not be easy to test the hardness of the silver flecks, but you could, perhaps, get some idea with a needle.  If soft, they just could be galena, if hard, possibly the light coloured form of pyrite.  Of course, there are lots of other things they could also be, but that's the fun of amateur mineralogy. :)

Have you tried scratching the brown parts?  (much easier way to streak than trying to use an unglazed tile, which often turns out to be softer than the specimen).  If the streak is red, think hematite. If it's light brown, go for limonite (easy to scratch) or goethite (if harder). 
 

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Re: trying to identify the metals in these rocks
« Reply #4 on: 01/11/2012 20:41:15 »

 

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