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

[MexicoDoug at aol.com]

_pierremariepele at yahoo.fr_ (mailto:pierremariepele at 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 at 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  ?