[meteorite-list] Question about NWA 869

From: Zelimir.Gabelica at uha.fr <Zelimir.Gabelica_at_meteoritecentral.com>
Date: Fri, 04 Nov 2011 09:19:12 +0100
Message-ID: <20111104091912.ku7nl6jryohwcg0o_at_w3mail.univ-mulhouse.fr>

Hi Melanie, Doug, list,

Doug, your reference is very appropriate.

In cataloging my collection, in some specific cases, when I feel the
meteorite I am describing is important, I use to add a short
introduction summarizing its historical and scientific background.

Here is my write-up for NWA 869, hoping it be of help to Melanie:

------------------

NWA 869 (Algeria, L3-6 rbr)(S3W1), found 2000, tkw: many++ at 7+ tons.

History and scientific significance.

It appears quite clear that meteorite collectors in Northwest Africa
have discovered a large L chondrite strewnfield at an undisclosed
location, most probably around Tindouf, Algeria. Thousands of stones
has been sold under the name NWA 869 in the market places of Morocco
and around the world, totaling about 7+ metric tons (April 2008,
confirmed by J. Kashuba in: ?Meteorite Times, Micro Visions?, March
2010), thereby making it one of the largest tkw?s to come out of NWA.

The corresponding meteorid was supposed weighing about 110 tons (4+m
in diameter), suggesting important ablation and fragmentation (Metzler
et al., LPS, 2008; Welten et al., LPS Conf. abstract, 2010, pp 2611).
Individual masses are known to range from <1 g to >20 kg.

This meteorite was classified a number of times by different
institutions (e.g. L4, that became later L5 ?UCLA, also L3.9-6 or L6?
brecciated or not), before the above final classification by A. Rubin.

It is certain that NWA 869 is paired with other NWA meteorites
although no systematic survey has been done.
Among many examples cited are NWA 787, NWA 900, SAH 02500 (?Wadi
Mellene?), possibly also ?AC-001?(see the 2 samples named ?NWA-aaa?
below still under investigation since its find in 2000) and likely
many, many more.
One other famous example is NWA 904 (L5 br, also S3 W1), of which the
numerous pics reported in MetBull database are strangely similar to
those of NWA 869, further confirming the similarity of the samples of
both meteorites in this collection .

It is also possible that some stones sold as NWA 869 are not part of
the same fall, although dealers are confident that most of the known
masses are sufficiently distinctive from other NWA meteorites in terms
of surface and internal appearance, so that the error rate should be
fairly low.

Although the source of the NWA 869 samples of this collection is
reliable (purchase by "MV" in a Moroccan ?selected reliable place?
where it has been confirmed that the origin is Algeria, just as for
NWA 904 (MV, personal communication), it is suggested (MetBull) that
scientists are advised to confirm the classification of any specimens
they obtain before publishing results under this name.

Much info was published regarding the composition of that strange and
very attractive meteorite.
When cut and polished, the matrix is full of color and chondrules of
all size, some armored. Literature reports 74% gray matrix, 20% light
tan (oxide staining) texture (type 5/6 clasts), 4% shock-darkened
sulfide-impregnated matrix, 1% type 3 clasts, <1% achondritic textured
clasts.
J. Kashuba (Met. Times, 03/ 2010) suggests it being a regolith
(coarse) breccia (asteroid soil) with chunks > 5.5 cm (Kashuba?s
picture in above reference; see also the extraordinary dual lithology
of the 27.30 g sample described below), also containing rare foreign
carbonaceous fragments.
Some pieces also display large metal grains and significant troilite
domains (35.42 g sample below).

The terrestrial age (4.4 ? 0.7 ky) is consistent with the low degree
of weathering, W1.
Since the abundance of regolith breccias among L-chondrites is only
~3% [Welten et al., 2010)], NWA 869 represents a rather unique and
large sample of the lithified regolith of the L-chondrite parent
body....
-----------------

Best wishes,

Zelimir



MexicoDoug <mexicodoug at aim.com> a ??crit??:

> NWA 869 represents an L chondritic regolith breccia containing
> preirradiated components. The meteoroid had an initial radius of
> about 2 m with a mass of about 110 metric tons. The transit time to
> Earth was about 4-5 Ma. Large variations of shielding depths between
> samples indicate that break-up of the meteoroid must have occured
> high in atmosphere. This would also explain the large inferred
> ablation loss, which is typical for large chondrite showers.
>
> Ref:
>
> "The L3-6 Regolith Breccia Northwest Africa 869: Petrology, Noble
> Gases, and Cosmogenic Radionuclides"
> Metzler, K.; Ott, U.; Welten, K. C.; Caffee, M. W.; Franke, L.
> 39th Lunar and Planetary Science Conference, (Lunar and Planetary
> Science XXXIX), held March 10-14, 2008 in League City, Texas.
> LPI Contribution No. 1391., p.1120
> Publication Date: 03/2008
>
> http://www.lpi.usra.edu/meetings/lpsc2008/pdf/1120.pdf
>
>
>
> -----Original Message-----
> From: Melanie Matthews <miss_meteorite at yahoo.ca>
> To: MeteoriteList <meteorite-list at meteoritecentral.com>
> Sent: Fri, Nov 4, 2011 2:10 am
> Subject: [meteorite-list] Question about NWA 869
>
>
> Hi list,
>
> Are there any estimates in how long ago this wonderful meteorite
> fell to Earth,
> and how large it might have been before it entered the atmosphere?
> It must have
> been a massive meteoroid, much larger than the one that produced the Buzzard
> Coulees.
>
> ?
> -----------
> -Melanie "MetMel" - avid meteorite collector/enthusiast from Canada!
> IMCA#: 2975
> eBay: metmel2775
>
>
> I eat, sleep and breath meteorites 24/7.
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Received on Fri 04 Nov 2011 04:19:12 AM PDT