[meteorite-list] How to test an iron meteorite ?

From: MexicoDoug_at_aol.com <MexicoDoug_at_meteoritecentral.com>
Date: Fri Dec 30 03:08:04 2005
Message-ID: <146.53435ddf.30e644d9_at_aol.com>

_pierremariepele_at_yahoo.fr_ (mailto:pierremariepele@yahoo.fr) writes:

>Is it necessary to make first a nickel test or go
>directly to the nitric acid test ?
 
Hola Pierre, you need to be clear to yourself first, what you want to do.

If you test it for nickel, you will know whether there is nickel in it.

If you dump a strong acid on an octahedral crystal, it will usually etch,
but what if it happens to be an ataxite or an anomalous meteorite without
Widfigs? The hexahedrite might have Neumann lines...maybe...if you recognize them
the first time through the drill...

So, the informal investigation you propose rests on your judgements to make
you satisfied, because you will decide in the end what you want to know about
your unknown! A formal analysis will need to be a little more, and a good
factorial experimental design I bet would test for nickel first (actually it
would send it to a lab with good equipment).

To etch, make "one molar" nitric acid if you can with alcohol, if not then
you can use with distilled water. Or you might just buy the 1 molar chemical
reagent straight (they use distilled water if it is a chemical supply house
w/reagent grade). Make sure you know how to properly mix reactive acids. You
don't want to have anything like my fuming nitric acid scar. It's nice now,
but it was like alien was coming out of me as I rinsed it under the safety
wash station. And I was covered and even with a complete face
shield...careful as you seem unpracticed...maybe you should use ferric chloride!

1 molar acid is one mole per liter. That's a standard acid concentration to
etch, but not a magic number. The formula for nitric acid is HNO3 =
1+14+16*3=63 g in a mole. If you start out with concentrate 16 M acid (very
cautiously) dilute it with 15 parts alc or water. Always add acid to water, not the
reverse. These dilution numbers are approximate as if you were preparing a
nice dinner. You could etch with 2 molar and you could get good results,
too. This is nothing to obsess about.

If the etch solution is a little warm, that is better, but you don't have to
warm it - it will etch at ambient temp, just take a little longer. Use
safety glasses that have side protection from splash, and minimize the exposure
time of the iron to the acid. Nitric acid isn't like hydrochloric acid. A
little HCl won't blind you, but Nitric maybe could turn your eye to ugly green
gel. Be sure you do it in a very uniform manner. If you have typical
plastic or neoprene tweezers, that is best. Obviously you need to know how to cut
and polish irons first, unless you want etched metal blobs. Etching is just
the merengue on the lemon pie. The cutting is the pain. Funny shapes aren't
bad but everyone doesn't see eye to eye on that comment...Put your polished
piece in the acid and after a couple of minutes the figures of the
octahedrite will appear like developing a negative in photography.

Take it out carefully when it is approaching the etch level you like. Rinse
soak it in pure alcohol (isopropyl, methyl or ethyl, doesn't matter here or
before) for a few minutes. Then soak it for about 15 minutes in fresh pure
alcohol. Repeat this again if you are serious about the piece. Then let it
soak in pure alcohol overnight in a capped tight bottle, having fun shaking it
inside if you have a midnight snack.

Take out the etched specimen and put in an oven at say, 60 deg C. Not more.
 You don't want to heat it too much or you broil the surface and oxidize the
fresh exposed metal. Over a half hour in the oven until you feel good about
it for small slices. You could use an IR lamp, too (a.k.a., heat lamp).
They are cheap in many hardware stores.

Don't coat it with anything unless the meteorite is a hopeless case without
coating: Coatings will only seal what's inside in and not all collectors
want them. There are other storage options...

I'm sure this is better covered in the archives. A note: If you etched
Sikhote-Alin the bands are so thick, you might need a larger specimen before you
can notice any figures...

Bonne Chance, Doug

_pierremariepele_at_yahoo.fr_ (mailto:pierremariepele@yahoo.fr) writes:
I have to analyze an iron (we are nearly sure it's a
meteorite) but I have to determine wether it's an
octahedrite or an hexahedrite.

Is it necessary to make first a nickel test or go
directly to the nitric acid test ?
 
Received on Fri 30 Dec 2005 03:07:53 AM PST