Dear List Members,
Yesterday I announced my new NomCom Approved Angrite which has a different
lithology than the other known angrites. It is NWA 4590 "Tamassint" and is a
Plutonic Angrite. For those who do not want to go to eBay to look up the
complete information, here is the approved classification and a link to an
abstract. This new angrite is gorgeous!!
Link to Lunar and Planetary Science Conference abstract on NWA 4590:
http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1522.pdf
Here is the NomCom Approved classification submitted to the Meteoritical
Bulletin:
==================================================================================
Northwest Africa 4590
Morocco/Algeria
Find: June 2006
Achondrite (angrite)
History: Scattered fragments from a small stone which appears to have
shattered upon landing recently were found covering an area of ~40 m2 in the
Morocco-Algeria border zone, 21 km SSW of Tamassint oasis and 18 km S of
Agoult, Morocco. Greg Hupé purchased all the recovered material in June
2006 from a Moroccan dealer in Tagounite. He then traveled to Morocco and
was shown the location by the original finder, and measured GPS coordinates.
Physical characteristics: Fragments totaling 212.8 g of a very friable
specimen composed of coarse yellow-green, black and white grains; very fresh
with preserved shiny, black fusion crust on some pieces, and minor pale
orange terrestrial weathering coatings on some broken surfaces.
Petrography: (A. Irving and S. Kuehner, UWS) Coarse grained (mostly 0.6-1.6
mm, but some olivine grains up to 12 mm) with a plutonic igneous (cumulate)
texture, and composed of clinopyroxene (33%, with rare pigeonite exsolution
lamellae), pure anorthite (28%), olivine (14 %, with prominent subparallel
exsolution lamellae (10-50 microns wide) of kirschsteinite), kirschsteinite
(5%, with thin exsolution lamellae of olivine), ulvöspinel (18%), and
accessory glass, troilite merrillite, Ca silicophosphate and metal
(kamacite). Some anorthite occurs as subhedral grains partially enclosed
within large ulvöspinel grains, but most occurs as intercumulus aggregates.
Clinopyroxene is strongly zoned with paler colored, corroded cores
surrounded by darker purple-brown mantles and distinct rims. Thin (5-50
microns wide) discontinuous, curvilinear zones of glass are present on some
grain boundaries (notably those between anorthite and ulvöspinel, but also
around and cutting across troilite grains), and are associated with
secondary clinopyroxene, kirschsteinite, olivine, anorthite and troilite
grains; these films of glass+daughter minerals truncate kirschteinite
exsolution lamellae in adjacent olivine. This angrite is unlike other known
specimens, having neither a fine grained quench or ophitic/intesertal
basaltic texture nor a coarse metamorphic texture (Irving et al., 2006;
Kuehner et al., 2007).
Geochemistry: Clinopyroxene (Fs20.8-33.3Wo53-54.9, FeO/MnO = 85-278),
olivine host (Fa72.6-74.7Ln3.5-3.6, FeO/MnO = 70-87), kirschsteinite
lamellae (Fa44.7-45.4Ln46-47.2, FeO/MnO = 73-82), kirschsteinite host
(Fa46.6-47.5Ln43.6-45.5, FeO/MnO = 63-68), olivine lamellae
(Fa75-76.7Ln2.7-2.8, FeO/MnO = 71-74). Oxygen Isotopes (D. Rumble, CIW):
analyses of two aliquots of acid-washed mineral fragments by laser
fluorination gave, respectively, d18O = 3.845, 3.881; d17O = 1.927, 1.967;
D17O = 0.0956, 0.0745 per mil.
Classification: Achondrite (angrite).
Specimens: A total of 20.01 g of sample, two polished thin sections and two
polished mounts are on deposit at UWS, and 4 g at Harper. Mr. G. M. Hupé
holds the main mass.
Irving, A. J., Kuehner, S. M., Rumble, D. and Hupé, G. M. (2006) A fresh
plutonic igneous angrite containing grain boundary glass from Tamassint,
Northwest Africa. EOS, Trans. Amer. Geophys. Union 87, Fall Meet. Suppl.,
Abstract P51E-1245.
Kuehner, S. M. and Irving, A. J. (2007) Grain boundary glasses in the
Tamassint plutonic angrite: Evidence for rapid decompressive partial melting
and cooling on Mercury? Lunar Planet. Sci. XXXVIII, Abstract #1522.
==================================================================================
Here are some links to photographs of NWA 4590 "Tamassint":
Group image of NWA 4590 "Tamassint":
http://www.lunarrock.com/nwa4590/nwa4590group.jpg
Microscopic image of matrix at 12x magnification::
http://www.lunarrock.com/nwa4590/nwa4590micro.jpg
Close-up image of fusion crust at 10x magnification:
http://www.lunarrock.com/nwa4590/nwa4590crust.jpg
Optical thin section image in cross-polarized light showing kirschsteinite
and olivine (blue to green), clinopyroxene (yellow-brown to dark grey),
intercumulus anorthite (white to pale grey) and ulvöspinel (black). Width of
field is 2cm:
http://www.lunarrock.com/nwa4590/nwa4590xpl.jpg
Thank you for looking and enjoy!
Best regards,
Greg
====================
Greg Hupe
The Hupe Collection
NaturesVault (eBay)
[EMAIL PROTECTED]
www.LunarRock.com
IMCA 3163
====================
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