Primitive Asteroids: Expanding the Range of Known Primitive Materials - 35 Seasons of U.S. Antarctic Meteorites - page 186

abundant amphibole and biotite, water-bearing minerals
not previously reported in any other chondrites. The
amphibole and biotite are nearly pure hydroxyl species.
Additionally, hydrogen in the amphibole is isotopically
heavier than any other known H reservoir, with D values
of +3660‰. The origin of the water in LAP 04840 is not
clear. It may have been derived from internal heating of
organics that accreted with the R chondrite matrix, or it
was delivered to the parent body from an outside source,
such as a comet or water-rich asteroid [ Trieman et al .,
2007; McCanta et al ., 2008].

(L/LL 3.05) [ Nittler et al ., 2008]. Presolar grains have been
found in Antarctic samples of all the major classes of
chondrites (O, C, and E), and these samples are highly
requested. The search for new types and more extreme
examples of existing types of grains can provide important
constraints on the stellar and galactic processes operating
prior to and during the birth of our solar system.

4.8. CONCLUDING REMARKS

The ANSMET meteorite collection has greatly
expanded our knowledge of primitive solar system mate-
rials. The examples described in this chapter only scratch
the surface. For example, not discussed in detail are the
CM chondrites; 413 of the 458 currently known CM
chondrites are from Antarctica. Although many are
paired, the Antarctic collection clearly provides a major
source of material for studying this important chondrite
group and understanding the asteroidal process of
hydrous alteration they record. Continued recovery of
new meteorites by ANSMET teams is essential to fur-
thering our understanding of the primitive materials in
the asteroid belt and to deciphering the clues they hold
about stellar processes, early solar system evolution, and
geologic processes on primitive asteroids.

4.7. PRESOLAR GRAINS

Some primitive Antarctic meteorites have preserved par-
ticularly well presolar grains that have contributed to our
understanding of nucleosynthetic and early stellar processes.
Presolar grains were formed by processes prior to the
formation of our own solar system. Presolar silicate and
oxide grains fall into four groups: groups 1 and 3 form in
red giant stars, and groups 2 and 4 form around low-mass
asymptotic giant branch (AGB) stars. Group 4 grains may
form in supernovae.
The primitive CO3 ALH 77307 (Plate 15) first showed
evidence for presolar diamonds [ Huss et al ., 2003], and
subsequent work has revealed additional material (silicates
and oxides) from the same meteorite [ Nguyen et al ., 2010].
Most of the grains condensed in low-mass red giant and
AGB stars, but some are from low-metallicity, low-mass
stars, others are from supernova outflows [ Nguyen et al .,
2010], and a few can offer constraints on galactic chemical
evolution.
Presolar grains have also been found in the CRs QUE
99177 and MET 00426. The matrix-normalized presolar
SiC abundances in these two CR chondrites is consistent
with abundances determined for the more heavily hydrated
CR1 and CR2 chondrites, showing that aqueous alter-
ation does not easily destroy presolar SiC. QUE 99177 and
MET 00426 contain high abundances (~120 ppm) of car-
bonaceous matter with anomalous C isotopic composi-
tions that probably formed in cold molecular clouds via
ion-molecule reactions [ Floss and Stadermann , 2009].
C-anomalous material of interstellar origin has previously
been found in interplanetary dust particles and in insol-
uble organic matter from primitive meteorites; however,
the amounts observed in QUE 99177 and MET 00426 are
significantly higher than in other primitive meteorites and
attests to the very primitive nature of the two CR3 chon-
drites [ Floss and Stadermann , 2011].
The small EH3 chondrite ALH 81189 has also yielded
presolar silicate grains [ Ebata et al ., 2006] of Group 1
affinity (AGB stars). Finally, presolar grains have been
found in the low-grade ordinary chondrites QUE 97008
(Plate 4), WSG 95300 (Plate 1), and MET 00452 and 00526

Acknowledgements . C. Alexander is thanked for doing a
thorough reading and review of an earlier version of this
chapter.

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