[meteorite-list] The EL3/Aubrite/whatever - Why FOSSIL?

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Sun, 02 Dec 2007 09:06:36 -0500
Message-ID: <OFDB42A9CA.2FF8BF1B-ON852573A5.004D9E27_at_usgs.gov>

It seems to me that there are at least four or five different things
that people may be trying to describe using various terms, including
"fossil" and "paleo". 1) The original minerals in a meteorite may be
partially or completely converted to terrestrial minerals on
earth. 2) During alteration and weathering, original textures may or
may not be pseudomorphed by secondary minerals. 3) A meteorite may
have a very old terrestrial age. 4) A meteorite may become buried in
terrestrial sediments. 5) The sediments in which a meteorite is
buried may become lithified.

There are lots of combinations possible among the above. Brunflo and
Osterplana meteorites have been buried, lithified, pseudomorphed, and
have extremely high terrestrial ages. The (as yet unofficial)
Morokweng stone has been buried, lithified, has an old age, but
retains much of the original mineralogy. The Eltanin meteorite also
retains much of its mineralogy, is old, but was deeply buried in
unconsolidated sediment, not rock. Highly oxidized iron meteorites
may consist entirely of terrestrial minerals, with no pseudomorphing,
no burial in sediment, and young ages. Some antarctic meteorites
have terrestrial ages of several million years, with no burial in
sediment at all, and retain their mineralogy.

In this context, what do the various terms that are being tossed about mean?

"Paleo" means old or ancient. But how old does a meteorite have to
be to get the moniker "paleometeorite?" I don't know. Is 10,000
years enough, as in the term paleolithic? If so, lots of Antarctic
meteorites are paleometeorites, as are quite a number of hot desert
meteorites. I think that to be useful, this term needs to only refer
to terrestrial age, and not be linked to burial or weathering.

The term "relict meteorite" is fairly well-defined by the
Nomenclature Committee in its Guidelines for Meteorite Nomenclature:
"...highly altered materials that may have a meteoritic origin [are]
designated relict meteorites, which are dominantly (>95%) composed of
secondary minerals formed on the body on which the object was found.
Examples of such material may include some types of "meteorite
shale," "fossil meteorites," and fusion crust." Note that this term
is independent of an object's age or whether it was buried.

"Fossil meteorite," used above, has never really been defined, but is
has been mostly applied to things like Brunflo and Osterplana, where
traces of highly altered meteorites are found in rocks and ancient
sediments. However, it has also been used as a synonym for highly
weathered meteorites found at the surface of the earth. I think that
it may be possible to come up with a rigorous definition, but I
suspect that if I did it, people would object. To be useful, I would
suggest that this term should be defined to reflect incorporation
into a rock or ancient sediment, and be independent of the degree of
alteration or mineral replacement.

Bottom line: I think a set of useful terms could be defined, but for
now the only one with a rigorous meaning is "relict meteorite." The
others are basically fluff.

jeff

At 11:18 PM 12/1/2007, dean bessey wrote:
>I dont want to get involved in the thread about what
>the classification is (I will be pretty happy no
>matter what the proposed options are) but can somebody
>explain to me why its called a "Fossil" meteorite?
>I realize that the term "fossil" can be loosely used
>to describe pretty much any old stuff (You could even
>call a living person a "fossil" meaning a person with
>old fashioned stubborn views) but given that this is a
>scientific classification I would expect more rigid
>use of the term in a scientific standpoint.
>To become fossilized means that over a long peroid of
>time (Usually millions of years) actual organic
>material gets replaced by stone so that when you have
>a fossil such as a dinosaur tooth, fossil shark tooth
>or ammonite you actually have a rock and not a real
>creature. No DNA can be extracted since its only a
>rock. Thats why we dont even know if dinosaurs were
>warm or cold blooded. We are only studying a rock when
>we study dinosaur fossils - not a real original
>artifact. So called mammoth tusk fossil or 10,000 year
>old fossil buffalo bones are not really a fossil since
>you get the original item - not a fossilized version.
>Fossil insects and bacteria in amber is often not
>fossilized even if millions of years old.
>But the meteorite in question has not been fossilized.
>The chrondrules are real chrondrules and not a
>replaced with stone chrondrule. You are not getting a
>calcified stone when you buy this "fossil" meteorite.
>You are getting a real original meteorite (Even if
>highly weathered and oxidized).
>I realize that dealers (Including myself) call it a
>fossil or paleo meteorite but can somebody explain to
>me why it should be called a fossil (Or Paleo)
>meteorite?
>Thanks
>DEAN
>PS: If somebody wants 200 or 300 kilos of this email
>me for details
>
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Dr. Jeffrey N. Grossman phone: (703) 648-6184
US Geological Survey fax: (703) 648-6383
954 National Center
Reston, VA 20192, USA
Received on Sun 02 Dec 2007 09:06:36 AM PST