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Help identifying metal
  
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MikeHancho




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PostPosted: Apr 17, 2019 22:07    Post subject: Help identifying metal  

Hello all , I’ve found a nugget while metal detecting. I’ve calculated the g/cm^3 to be 1.87. It has a gray metallic streak. Hardness seems between 2-3. Not the slightest bit attraction to a magnet. I’ve looked up metals with that density range and can’t figure out what it is. Can anyone help me figure it out what it is? Found near the coast on the border of san Diego /Orange County.


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SteveB




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PostPosted: Apr 18, 2019 01:25    Post subject: Re: Help identifying metal  

Lead? Looks like the projectile from a bullet. Shows some telltale ballistics signs.
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MikeHancho




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PostPosted: Apr 18, 2019 01:46    Post subject: Re: Help identifying metal  

Isn’t lead more dense than 1.87g/cc?
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SteveB




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PostPosted: Apr 18, 2019 02:06    Post subject: Re: Help identifying metal  

Not all bullets use lead plus these days the greens have pushed for lead free projectiles. So its an alloy substitute instead. Google it, you have not found a natural nugget and how did you get an accurate density of a small item? Nothing I see says this is a natural specimen.
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MikeHancho




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PostPosted: Apr 18, 2019 09:07    Post subject: Re: Help identifying metal  

SteveB wrote:
Not all bullets use lead plus these days the greens have pushed for lead free proectiles. So its an alloy substitute instead. Google it, you have not found a natural nugget and how did you get an accurate density of a small item? Nothing i see says this is a natural specimen it only tells me its trash.


I highly doubt it’s a projectile
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MikeHancho




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PostPosted: Apr 18, 2019 09:10    Post subject: Re: Help identifying metal  

I used a graduated cylinder to measure the water it displaces and a scale to measure its weight in grams. D=m/v.
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Pete Richards
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PostPosted: Apr 18, 2019 09:47    Post subject: Re: Help identifying metal  

1.87 g/cc is a very low density for a metal, or for minerals in general, for that matter. Is it possible that this specimen has a lot of trapped void space - which weighs nearly nothing but displaces water?

The density is way too low for lead, or for that matter, for any other metal that would be used for projectiles, which some have suggested as the source of your material.

Most of the metals that have densities less than 1.87 are way too reactive to be found in nature as metals, and I don't believe any of them are recognized as minerals, though many of them are important constituents of minerals (e.g.sodium, potassium, and magnesium).

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John Cesar




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PostPosted: Apr 18, 2019 11:50    Post subject: Re: Help identifying metal  

I suggest that this object is a melted piece of aluminum. This is frequently the treasure found around old camp fires when metal detecting.
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Pete Richards
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PostPosted: Apr 18, 2019 13:03    Post subject: Re: Help identifying metal  

I thought of aluminum, too, but its density is 2.7 g/cc, almost 50% higher than the reported value. There would still have to be a lot of lighter stuff (including air) locked inside to get this low a reading. Still, aluminum is probably the best guess.

I would suggest that the density measurement be done again from the very beginning.

In any case, this is not a mineral.

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MikeHancho




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PostPosted: Apr 18, 2019 13:30    Post subject: Re: Help identifying metal  

Is there any sort of acid test or anything specific to aluminum I could try. I’ve done the density test with a piece of pure copper to rule out error of my testing.
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Pete Richards
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PostPosted: Apr 18, 2019 14:02    Post subject: Re: Help identifying metal  

Berry and Mason's Mineralogy (1959) lists the following test for aluminum in minerals (p. 264):

"Light-colored minerals which are infusible can be tested [for aluminum] by moistening an ignited fragment with cobalt nitrate solution and reheating. If aluminum is present, the mineral is colored deep blue."

The references to fusing and heating are with a blowpipe - a propane torch would do the job. Presumably, metallic aluminum would not require "ignition" beforehand - just heating it after dipping it in cobalt nitrate solution should develop the color. It would be a good idea to try this on a piece of known aluminum as well. Chemists on the list may wish to comment!

Of course, you have to have some cobalt nitrate....

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PostPosted: Apr 18, 2019 20:37    Post subject: Re: Help identifying metal  

So here’s an update , I’ve decided to take a mapp gas torch to it. I would guess it’s not aluminum being that mapp burns at 2,020F in open air. I couldn’t get it to completely melt and I tried for about 8 min. What do you think of the photos? Could it be my density measurement was way off?


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PostPosted: Apr 18, 2019 20:46    Post subject: Re: Help identifying metal  

* 2,020C
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alfredo
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PostPosted: Apr 18, 2019 21:06    Post subject: Re: Help identifying metal  

A simple test for aluminium, using more readily available chemicals, is to drop the lump into a warm solution of NaOH (aka "caustic soda", "liquid plumber", etc). Aluminium will be rapidly attacked, and bubble, whereas most common heavier metals will not. (Buy a white cane in advance, just in case you splash any into your eyes.)
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