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Question about terrestrialized specimens


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If an iron meteorite has oxidized due to weathering with little iron left and no widmanstatten pattern can be obtained is there a change from a meteorite to another classification for these specimens.

I have attempted to obtain widmanstatten from small nantans to no avail.

Your thoughts please.

Thank you

Rick

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I have always figured that if they have been consumed by oxidation that they were no longer meteoritictic. at least no more than a manganese bomb ot a niickel deposit.

it would be tough to class shale from an iron as anything but terrestrial. it all came in flying at some point and at some point had ceased to be meteoritic. i think when oxidation has erased the characteristics of et rocks and replaced them with earthly qualities it is no longer s space rock.

Edited by Bedrock Bob
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That's a good Question for sure. At what Point Does a Rock become a Rock and not a Space Rock. Everything is made from Star Dust.

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when the meteorite loses all identifying aspects of the type meteorite that it is, then it has been terrestrialized and of the earth not space...that can take a very, very long time for an iron and probaly not very long for a carbon type...

fred

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G'Day Rick

I think everybody's pretty well answered your question. As for a change in classification, that would be a negative. If the Nantan you are talking about is shale and it can break off in quite large flakes, your chances of producing a widmanstatten pattern (also known as Thomson Structures) would be a negative. With Nantan's running at 92%Fe and only 6.9% Ni, much has been consumed and turned into rust but it seems like there's a big market out there for this Nantan shale.

But others have brought up an interesting situation on whether a meteorite weathers enough to be terrestrial. This has been talked about often, referred to fossil or paleo. I have no comments here but I'll post some information for you.

However, the record of fossil meteorites (those with ancient terrestrial ages) is very meager, especially considering the amount of meteoritic material that has fallen in the last few hundred million years. An iron meteorite was reported in 1942 from Miocene sediments in Georgia; an iron meteorite was discovered in the 1950’s during the drilling of an oil well in Eocene rocks in Texas; iron meteorites having terrestrial ages of 3.1 and 2.7 million years (my) were discovered in Alabama and Chile, respectively; relict chondrules (small, spherical, remelted mineral inclusions) of stony meteorites have been reported from bauxites of Mesozoic age in the Ural Mountains of Russia; and in 1996 a nickelbearing meteorite fragment of Late Cretaceous age
was recovered from a sediment core in the northwestern part of the North Pacific Ocean.
A little bit on fossil / paleo
Cheers
Johnno
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Johnno, a new classification for fossil meteorites- I did not know about that. Thanks for the link. Many truths have changed, been revised or simply disproved in my life...that is the beauty of science and an excellent reason to keep learning and informed...

fred

Edited by fredmason
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Johnno, the link you provided references an Enstatite chondrite, not a true fossil meteorite (sometimes those E chondrites are mistakenly called fossil or paleo meteorites, so are some shale finds, but they are not actually fossil meteorite, they are different classifications).

Fossil, or Relic meteorites as they are classified in the MetBul, are very interesting. Here's the bits of info I've gathered on them:

"Fossil" meteorites are also known as relict meteorites and there are several listed in the MetBul: Relict meteorite classifications (the find circumstance write-ups on most of them are pretty interesting).

The only one with a picture in the MetBul is Brunflo:

brunflo.gif

The MetBul defines them as, "...composed mostly of terrestrial minerals, but are thought to have once been meteorites. Note: evidence that this was once a meteorite may not have been critically evaluated."

All of the Swedish ones were found imbedded in 480,000,000 year old limestone.

I came across this photo of some fossil meteorites on display at the Natural History Museum in Vienna. Source: http://pad39a.blogspot.co.uk/2013/04/meteorites-at-natural-history-...

20130407_153504.jpg

I also came across this paper on the Brunflo fossil meteorites (you may have to be a MetSoc member to view the full document):

http://onlinelibrary.wiley.com/doi/10.1111/j.1945-5100.2009.tb00720...

Abstract—
The Brunflo fossil meteorite was found in the 1950s in mid-Ordovician marine limestone in the Gärde quarry in Jämtland. It originates from strata that are about 5 million years younger than similar limestone that more recently has yielded >50 fossil meteorites in the Thorsberg quarry at Kinnekulle, 600 km to the south. Based primarily on the low TiO
2
content (about 1.8 wt%) of its relict chromite the Brunflo meteorite had been tentatively classified as an H chondrite. The meteorite hence appears to be an anomaly in relation to the Kinnekulle meteorites, in which chromite composition, chondrule mean diameter and oxygen isotopic composition all indicate an L-chondritic origin, reflecting an enhanced flux of meteorites to Earth following the disruption of the L chondrite parent body 470 Ma. New chondrule-size measurements for the Brunflo meteorite indicate that it too is an L chondrite, related to the same parent-body breakup. Chromite maximum diameters and well-defined chondrule structures further show that Brunflo belongs to the L4 or L5 type. Chromites in recently fallen L4 chondrites commonly have low TiO
2
contents similar to the Brunflo chromites, adding support for Brunflo being an L4 chondrite. The limestone in the Gärde quarry is relatively rich (about 0.45 grain kg
−1
) in sediment-dispersed extraterrestrial chromite grains (>63 μm) with chemical composition similar to those in L chondrites and the limestone (1–3 grains kg
−1
) at Kinnekulle, suggesting that the enhanced flux of L chondrites prevailed, although somewhat diminished, at the time when the Brunflo meteorite fell.

Edited by Mikestang
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I always thought the Sudbury complex in Canada was the result of a huge asteroid and is now a rich nickel deposit thanks to the weathering processes. At what point is it still considered a "fossil"? Or not?

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Whatever hit at Sudbury was vaporized on impact, there were no pieces left. Any concentrations of nickel there would be as a result of the impact itself (melting the Earth and concentrating metals/minerals that way), not remnants of the impactor. So far, true fossil meteorites (where the minerals have all been replaced here on Earth) have only been found in limestone deposits.

Edited by Mikestang
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