[meteorite-list] Two More Unique Martian Meteorites Found In Africa (NWA 998 and NWA 1195)

From: Matteo Chinellato <mcomemeteorite2000_at_meteoritecentral.com>
Date: Thu Apr 22 10:04:48 2004
Message-ID: <20020510043724.48831.qmail_at_web10307.mail.yahoo.com>

Another is in arrive.........
Regards

Matteo

--- Ron Baalke <baalke_at_zagami.jpl.nasa.gov> wrote:
>
> http://www.jpl.nasa.gov/snc/news48.html
>
> Two More Unique Martian Meteorites Found In Africa
> (NWA 998 and NWA 1195)
> Dr. Anthony Irving
> University of Washington
> May 9, 2002
>
> The fertile hunting grounds of the western Sahara
> have turned up two more
> Martian meteorites, bringing the total number of
> unpaired examples to 26.
> Both were recovered and confirmed by the same team
> of investigators based in
> Seattle (USA). Adam and Greg Hupe, in collaboration
> with Drs. Anthony Irving
> and Scott Kuehner at the University of Washington,
> acquired and analyzed a
> new orthopyroxene-bearing nakhlite (NWA 998) and a
> new olivine-phyric
> basaltic shergottite (NWA 1195), which were found by
> separate nomadic groups
> in western Algeria or eastern Morocco (full
> descriptions submitted to the
> Meteoritical Bulletin are given below). The new
> nakhlite (Images 1 and 2) is
> the sixth known example and has unique features
> including the presence of
> minor orthopyroxene accompanying the dominant
> subcalcic augite, intergrowths
> of titanomagnetite and low-Ca pyroxene (Image 3;
> suggesting a
> post-crystallization, high temperature oxidation
> event), and secondary
> carbonate, sulfate and possibly hydrous minerals
> (which may be products of
> weathering or other alteration processes on Mars).
> Oxygen isotope analyses
> by Dr. Douglas Rumble at the Carnegie Institution
> (Washington, D.C.) have
> confirmed its kinship with other Martian meteorites.
> The new basaltic
> shergottite, which has an unusual elongated shape
> and a distinctive
> weathering rind (Images 4 and 5), is the fourth
> known example of a subgroup
> (including DaG 476, SaU 005 and NWA 1068, and
> respective paired samples)
> characterized by relatively large olivine megacrysts
> in a finer grained
> groundmass composed mainly of pigeonitic pyroxene
> and shocked plagioclase
> (maskelynite). Scientists continue to debate whether
> some or all of the
> olivine megacrysts in these samples represent
> phenocrysts grown from the
> magma that produced the groundmass, or xenocrysts
> captured from subsurface
> rocks or mixed in from possibly related, partially
> crystallized subsurface
> magma batches. Most of the olivine crystals in NWA
> 1195 have well developed
> crystal faces suggesting that they are phenocrysts
> (Images 6 and 7), and the
> cores of the compositionally zoned olivine grains
> are the most
> magnesium-rich yet found in Martian samples
> (indicative of a relatively
> unfractionated magma from the interior of the
> planet).
>
> The successful recovery of these rare and important
> meteorites required a
> team approach among dealers, collectors and
> scientists sharing a common
> interest in their pursuit, preservation and study.
> The Martian stone now
> designated NWA 998 was rumored to exist in Morocco
> as early as September,
> 2001 at a time when international travel was out of
> the question. Tucson
> dealers Mike Farmer and Jim Strope, trusting their
> sources, took this rumor
> seriously and played a key role in the acquisition.
> Adam and Greg Hupe were
> invited into the pursuit of this mysterious stone
> because of its extremely
> high asking price, although they held little hope
> that it actually existed.
> The Hupe brothers have invested considerable
> resources in the pursuit of
> other such fantastic stones only to come back empty
> handed. Once the stone
> was confirmed to really exist, a deal was finalized
> at the Tucson Gem and
> Mineral Show in February, 2002, where it realized a
> record wholesale price,
> many times more than any other meteorite purchased
> in this manner. This new
> nakhlite is believed to have been found in western
> Algeria, but this is hard
> to confirm because the Berber nomads will not
> disclose its exact location,
> and, despite a promised thorough secondary search,
> no more has been
> recovered.
>
> The recovery of shergottite NWA 1195 followed a
> different path. Adam and
> Greg Hupe spent months educating Moroccan dealers to
> look for unusual stones
> among batches of meteorites, and also to document
> which nomads found good
> stones so that additional pieces might be recovered.
> In the past, any stone
> that was not magnetic or lacked a fusion crust was
> usually cast aside and
> forgotten. The Hupe brothers financed the high costs
> of this untested
> recovery method with few results until a shipment of
> suspected meteorites
> arrived in Seattle in March, 2002. A 50 gram stone
> with no fusion crust was
> pulled from a group of terrestrial stones by Adam
> Hupe, who suspected that
> it might be a shergottite. The next day a thin
> section was prepared in
> excited anticipation by Dr. Anthony Irving and David
> McDougall at the
> University of Washington and revealed the
> characteristic presence of
> maskelynite. Full confirmation required expert
> electron microprobe analysis
> by Dr. Scott Kuehner. Since careful notes had been
> made on which nomadic
> group found this stone, a search for more of this
> material was initiated and
> within a week another 265 gram stone was recovered
> 15 meters from the
> original in the Safsaf region of eastern Morocco.
> Greg Hupe then embarked on
> a grueling 36-hour trip to Morocco and spent four
> days with nomads in the
> desert to retrieve the new find. Greg brought along
> the end portion cut off
> the 50 gram stone and was delighted when it fit
> perfectly to the newly
> acquired 265 gram stone, thus reuniting this
> meteorite with its broken
> counterpart after weathering separately for
> thousands of years.
>
>
>
> Image 1: Main mass of nakhlite NWA 998. Photo
> Copyright Adam and Greg Hupe.
>
> Image 2: Thin section image (11 mm by 6 mm) in
> partially cross-polarized
> light of NWA 998 showing abundant prismatic augite,
> olivine (green),
> orthopyroxene and titanomagnetite (black).
> Photo Copyright Adam and Greg Hupe.
>
> Image 3: False-color backscattered electron image
> of NWA 998 showing a
> symplectitic intergrowth of titanomagnetite (beige)
> and low-Ca pyroxene
> (green) at a contact between olivine (red) and
> titanomagnetite (beige)
> adjacent to plagioclase (blue). Photo Copyright
> Adam and Greg Hupe.
>
> Image 4: Assembled complete stone of shergottite
> NWA 1195 showing interior.
> Photo Copyright Adam and Greg Hupe.
>
> Image 5: Thin section image (29 mm by 19 mm) in
> plane light of NWA 1195
> showing the thin terrestrial weathering rind
> (reddish brown) and porphyritic
> texture, with large olivine phenocrysts (brown and
> yellow) in a groundmass of
> pigeonite (pale yellow) and maskelynite (white).
> Photo Copyright Adam and
> Greg Hupe.
>
> Image 6: Thin section of NWA 1195 in cross-polarized
> light showing euhedral
> olivine phenocrysts in a groundmass of pigeonite
> (yellow) and maskelynite
> (black). Photo Copyright Adam and Greg Hupe.
>
>
>
> Descriptions Submitted for Publication in the
> Meteoritical Bulletin
>
> Northwest Africa 998
> Algeria or Morocco
>
=== message truncated ===


=====
M come Meteorite - Matteo Chinellato
Via Triestina 126/A - 30030 - TESSERA, VENEZIA, ITALY
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Received on Fri 10 May 2002 12:37:24 AM PDT