[meteorite-list] Disappointed collector

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 09:43:30 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C8698E5502_at_US-Torrance.mail.saic.com>

Hi Paul,

You wrote, in part:

> What Im really trying to say here is that it should be officially
recognised
> and classified before it can be called a meteorite and anything less than
> that is just speculation and an educated guess.

With a cut surface, or even one that is simply ground down
a little bit to reveal the interior, you can in most cases
remove all speculation and doubt -- even if you aren't an
expert. With unclassified Moroccan/Algerian meteorites,
more than 95% of the time you're talking about ordinary
chondrites, and a cut surface will show metal flecks and
often times chondrules. If so, it's a slam dunk.

> Personal opinions are different though I cant see how I can be content to
> have something in my collection that is only PROBABLY a meteorite. Even
> if its got a high certainty and an experienced seller says it is genuine I
> dont think Id be happy with that if its not OFFICIALLY recognised.

It's important to make a distinction between "identification"
and "classification". It is usually a rather trivial matter
to positively identify a meteorite. Classification, though,
is another matter. There are ~degrees~ of classification,
of course. You obviously would have no difficulty distinguishing
an iron meteorite from a stony one or a stony-iron. (With
unclassified NWAs, I think we can safely say we're talking about
stony meteorites.) With stony meteorites, you can take it
one step further and subdivide into chondrites vs. achondrites.
(Consider yourself extremely fortunate if you should begin to
suspect that you have one of the latter!)

With a hand lens and a cut and polished surface, you can subdivide
the ordinary chondrites further still: equilibrated and *possibly*
unequilibrated. I emphasize "possibly" because it is not easy
for an amateur to tell the difference between a petrologic
type-3 and a good type-4 chondrite.

Finally, you may be able to make an educated guess as to whether
a chondrite is an H-, L- or LL- chondrite (I don't mention
carbonaceous or rarer types because of the unlikelihood of you
buying one that was missed by the seller). The rarer LL's are
only weakly attracted to a magnet, and so you can often
differentiate them from the H's and L's (as can the dealers, so
again you're not likely to get one by accident). But H- vs. L-
chondrite can be tough. Here, the comparative magnetic attraction
can throw you off. The size, shape and distribution of metal
will often allow you to make a good educational guess, but not
always -- especially if the meteorite is heavily weathered. This
is why some dealers will go so far as to identify a specimen as
an "H or L ordinary chondrite."

So, you see, there's a lot you can determine without a complete,
formal classification.

> This discussion group is always very quick to criticise sellers on
auctions
> who sell rocks advertised as only MIGHT be a meteorite and ask the seller
> for information on its name and type and then ridicule the seller for not
> having this information to hand.

More often than not, the criticism is directed at sellers
who are trying (perhaps innocently) to pass off an obvious
terrestrial rock as a meteorite. Again this gets back to
identification vs. classification. There's a big difference
between selling a meteorite without classification or find
location, and advertising a piece of slag/hematite/magnetite
as a meteorite.

> I know many of you can recognise a meteorite after you've cut it open but
> what about its type?

(See above).

> And doesnt knowing when and where it fell and its groupings or pairings
have
> some added interest to?

Absolutely -- the more you know, the better. But for the many
reasons you've seen discussed on this list, you just won't have
this information for a lot of the western Saharan meteorites.

So don't be overly discouraged by the unidentified, unclassified
meteorites you've purchased so far. Explore them! You get the
excitement of positively IDing them yourself, and trying to
sleuth out as much about their classifications as you can using
just your eyes, a magnifier, a magnet and a polished surface.
You'll learn a lot. Who knows? You might have something
interesting hiding in your purchases that warrants a full
classification.

Best wishes,
Rob Matson - amateur meteorite aficionado
Received on Mon 09 Jul 2001 02:29:45 PM PDT