[meteorite-list] Recognizing a Venusian meteorite

Sterling K. Webb kelly at bhil.com
Fri Oct 24 21:38:09 EDT 2003 

Hi,

    Actually, there are a number of sedimentary meteorites. It's just that
they are not acknowledged to be meteorites.
    If you have the CDROM of the Catalogue, have the software assemble you a
list of "pseudometeorites" that are not irons.
    Or just search for BLECKENSTAD (April 11, 1925) SWEDEN, a sedimentary
meteorite of white limestone complete with fossil shells. It was reported on
by Dr. Assar Hadding of the Swedish Geological Institute in 1939 who after a
long investigation decided it really was a meteorite. The chief reason for
so believing is that it is a WITNESSED FALL and you really can't get much
better than that. However, he was widely regarded as whacky by the wise men
of 1939 and (equally wisely) shut up about it for 20 years. Hadding was so
discouraged by the reception of his earlier paper that, when he discovered
another sedimentary meteorite, he threw it away! Only much later, when he
realized that they could have been "Earthites," did he write about the two
stones again.
    Nininger himself found a small sedimentary meteorite, on March 24, 1933,
while searching for fragments of Pasamonte. The stone in question was a
dirty grey  limestone with fragmentary shell bits fossilized in it and
sporting a black fusion crust. He ruled out an artificial origin for the
crust but was unwilling to claim it was a meteorite, apparently not because
he didn't think it was a meteorite but because it wasn't worth the noise...
    Frank Cross wrote about sedimentary meteorites at length in the journal
"Popular Astronomy" (Vol. 55, 1947, pp. 96-102), citing Trevlac (Indiana)
and Montrose (West Virginia), two independently discovered sedimentary
meteorites with identical green glassy crusts.
    And so it goes...
    The whereabouts of most of the sedimentary "pseudometeorites" is
unknown, not surprising considering their reception, so the sophisticated
tests that could be performed today are impossible. There's a kind of
self-reinforcing judgement at work in that. Two guys from the French
Academy, flumping their powdered wigs, explain, "Foolish peasant! Ze
sedimentary rocks from ze sky, zey do not fall," so we throw the evidence in
the trash.
    Anybody on the List know what happened to Nininger's sedimentary find?


Sterling K. Webb
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mark ford wrote:

> More to the point where are all the earth meteorites? We should be able
> to recognize them, (one would hope!), I guess as most of the earths
> immediate surface is soil, or sedimentary rock(s), an earthite meteorite
> would be pretty strange do date no true 'sedimentary' meteorites have
> been found?, I guess it would probably look like a tektite I.e silica
> glass... or would they be just be highly shocked ordinary terrestrial
> rocks but with a fusion crust?
>
> Mark Ford
>
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"A far more challenging prospect for those interested in studying planetary meteorites is the quest for samples of sedimentary origin. Throughout the history of meteoritics, materials of this nature have been documented many times; in fact, they are so well established that the different categories have names [2,10], e.g. "amathosites" and "calcarites" are sandstone and limestone meteorites respectively. However, it has to be concluded that whatever samples are currently represented in the world's collections, they are most probably pseudometeorites (i.e. samples of terrestrial origin which, to some people at least, look like meteorites on account of their water- rounded surfaces, or coatings of desert varnish, etc.). The celebrated calcarite, Bleckenstad [11], is purported to contain fossils. But, a terrestrial rock could still be a meteorite. Indeed, Melosh and Tonks [12] have shown that some impact-ejected terrestrial materials could reside in space for 5 million years or so, before returning to the surface - these samples might be observed to fall, have a fusion crust, contain cosmogenically produced nuclides etc. It seems likely, though, that meteorite curators through the ages, having been presented with a fossiliferous sedimentary rock, would probably not have been able to assess the true nature of such a terrestrial meteorite (notwithstanding the protestations of the owner). How many of these types of sample have been returned to sender? More pertinently perhaps, how many such samples are still preserved in traditional collections?"Meteorite Searches
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