[meteorite-list] Anomalous CO3.05 - NWA 4530

From: Greg Hupe <gmhupe_at_meteoritecentral.com>
Date: Wed, 16 Dec 2009 17:32:56 -0500
Message-ID: <CEDA46AD52914B07A6C124B1CCDC1DD3_at_Gregor>

Dear List Members,

In light of today's discussion of pristine chondrites, I would like to take
this opportunity to announce Officially-named NWA 4530, an Anomalous CO3.05
Polymict Carbonaceous Chondrite. It is just one of a handful of this
intensely rare meteorite type.

Here is a quote from the primary researcher who analyzed NWA 4530:
"NWA 4530 is the most pristine early solar system material I have ever seen.
There are no CO3.05s or CO3.0s or even CO3.1s that are as pristine (W/0) as
NWA 4530... a unique and important meteorite!"

Here is the submitted classification for the Meteoritical Bulletin:

Northwest Africa 4530
     Algeria

     Find: September 2006

     Carbonaceous chondrite (CO3.05, anomalous)

History: A single 35.9gram stone broken into 5 pieces was purchased by Greg
Hup? from a Moroccan dealer in Tagounite in September 2006.

Physical Characteristics: Very fresh, light to medium gray interior, with
translucent dark fusion crust with internal bubbles and a prominent
diamond-shaped reticulated pattern in areas where the crust has flaked off.

Petrography (T. Bunch and J. Wittke, NAU; A. Irving, UWS): A polymict,
unequilibrated meteorite, exhibiting some characteristics consistent with
other CO3 chondrites (e. g., non-spherical chondrules are most abundant and
are lobate, distended, and highly irregular, some with fine-grained
accretionary rims). Distinctive chondrule-like objects (designated as CLO)
are also common and are typically fragmented with miniscule mesostasis.
Classic chondrule types are few in number and consist mostly of densely
packed Type I PO and POP with little to no detectable mesostasis. There is
no apparent correlation of Cr2O3 with FeO in FeO-rich olivine with distance
from core to rim, yet there is a correlation of Cr2O3 with FeO in
forsteritic cores. Cr-rich olivine rims were not observed. Amoeboid olivine
inclusions are the most common CAI. The fine-grained matrix is
unrecrystallized with very fine-grained magnetite, sulfides, silica,
glasses, and silicates. Rare, small cohenite grains were also found.
Irregular-shaped sulfides are much larger and range in size from 0.02 to
0.12 mm. Complex nuggets are of two types: (1) those consisting of
pentlandite, troilite, and Cr-magnetite, and (2) sulfide-bearing nuggets,
consisting of a solitary pentlandite grain surrounded by troilite with wispy
oriented inclusions of an unknown sulfide. Magnetite is a common inclusion
in chondrules, and the composition and distribution of magnetite is similar
to that in CK chondrites. No NiFe metal was observed anywhere. Angular,
large (up to 2 x 1.5 mm) igneous-textured clasts contain (in vol %):
forsterite, 79; troilite and pentlandite, 18 and diopside, 3.

Geochemistry: Overall olivine compositions range from, Fa0.03 to Fa72
(FeO/MnO = 61 - 133, mean is 91). Cr2O3 in FeO-rich olivine fragments has a
range of 0.10 to 0.48 wt % with a peak at 0.34 wt % (N = 84). Chondrule-like
fragments (CLO) have a more overall FeO-rich olivine composition, with lower
Fa range (core Fa = 4; rim Fa =41) and lower Cr2O3 content (0.04 - 0.31,
mean = 0.18). Chromian spinel, Cr/(Cr+Al) = 0.24 -0.34. Unknown sulfide is
(in wt. %): Fe, 67.5 and S, 33.2. Cr-magnetite contains 0.47 - 3.1 wt %
Cr2O3 with minor amounts of MgO, Al2O3, P2O5, CaO and NiO. Unzoned
igneous-textured clast olivine is Fa2.7 (FeO/MnO = 31) and diopside is
Fs1.2Wo39. Average matrix analysis (partial, N= 27) by defocused beam
microanalysis is (in wt %): Na2O = 0.81; K2O = 0.25; S = 2.48; P2O5 = 0.44;
Cr2O3 = 0.45; NiO = 0.45; S/Si = 0.19; Na/Al = 0.31. Oxygen isotopes (D.
Rumble, CIW): analysis of acid-washed material by laser fluorination gave
d18O = -4.228; d17O = -7.052; D17O = -4.829 per mil, consistent with CO
chondrites.

Classification: Carbonaceous chondrite (CO3.05, anomalous). This stone is
polymict; most components are consistent with CO3 chondrites, although
chondrule-like components (CLO) are not common in CO chondrites (from a
survey of 34 specimens in the NAU repository). NWA 4530 is more highly
oxidized than most CO chondrites and is devoid of metal. The Cr2O3 content
in olivine and the matrix composition is consistent with CO3.0 - CO3.05
(Grossman J. N. and Brearley A. J. (2005) M&PS 40, 87-122). The weathering
grade is W0/1; there is no evidence of any interior weathering. The shock
level is S1.

Type specimens: A total of 6.4 g and one polished thin section are on
deposit at UWS. Mr. Philip Mani is the main mass holder.



Best regards,
Greg


====================
Greg Hupe
The Hupe Collection
NaturesVault (eBay)
gmhupe at htn.net
www.LunarRock.com
IMCA 3163
====================
Click here for my current eBay auctions:
http://search.ebay.com/_W0QQsassZnaturesvault
Received on Wed 16 Dec 2009 05:32:56 PM PST