Geology Reference
In-Depth Information
The macroscopic descriptions made at JSC and the
microscopic descriptions made at SI are combined and
announced in the
Antarctic Meteorite Newsletter
, which
is released twice a year. These announcements are also
coordinated with the Meteoritical Society's Nomenclature
committee, which approves newly proposed meteorites.
The classification and announcement process has
always provided the minimum amount of information to
formulate a definitive classification, allowing the scientific
community to make informed requests for meteorite
samples. This also ensures that the scientific investiga-
tions are left to the science community rather than under-
taken (either in whole or in part) by the curators
overseeing the collection. For example, oxygen isotopic
measurements, although frequently used for classification
of meteorite samples, are not usually necessary because a
variety of other mineral and textural information can be
used to make an accurate classification. Therefore, oxygen
isotopic data are only obtained for samples for which tex-
tural and mineral data do not allow a definitive
classification to be made. For many years Robert N.
Clayton and Tosh Mayeda [
Clayton and Mayeda
, 1996]
provided oxygen isotopic analyses to support the collec-
tion in this way, and in more recent years some analyses
have been contributed by James Farquhar (Univ.
Maryland), Doug Rumble (Carnegie-DTM), and
Zachary Sharp (UNM). When new data are published
making it clear that a sample has been misclassified,
reclassifications are announced in the
Antarctic Meteorite
Newsletter
and also updated with the Meteoritical Society
meteorite database.
Iron meteorites and pallasites are stored at the
Smithsonian Institution in the National Museum of
Natural History in Washington, D.C. They are stored in
dedicated auto-desiccators (Figure 3.2) near facilities
uniquely equipped to cut and prepare irons and predom-
inantly-iron-bearing samples.
3.2.5. Requests, MWG, MSG, and Allocations
Sample requests and allocations were designed to be
less stringent than those developed for
Apollo
samples to
increase accessibility to the collection for the scientific
community. JSC curator Don Bogard and his staff strove
to make the Antarctic meteorite allocations process more
streamlined and efficient compared to the
Apollo
sample
allocations. The JSC curator can approve sample requests
unless they fall into one of the following categories: a new
PI, a newly announced sample, a piece of a small (<20 g)
meteorite, a larger piece (> 5 g) of a single meteorite, or a
meteorite on the special list (see below). Sample requests
from these five categories must be reviewed by the
Meteorite Working Group (MWG), a panel of meteorite
experts providing advice to the curators, and the Meteorite
Steering Group (MSG), a body composed of member one
from each of the three agencies involved (SI, NASA, and
NSF) that approve the recommendations of MWG mem-
bers. Early MWG meetings were long and focused on
infrastructure needs, planning, funding, and rules, while
later meetings have focused more on brevity and resolving
decisions on the many requests received annually.
A great challenge facing curators Glenn MacPherson
and Marilyn Lindstrom in the 1980s and early 1990s was
to oversee a collection that was quickly growing in size,
using an unchanged amount of personnel support and
resources. During this time frame, the allocation guide-
lines changed as the collection matured in size and diver-
sity (lunar and martian meteorites, many new chondrite
groups, and some rare and unusual achondrites). They
managed to strike a balance between the popularity and
great demand for the samples being characterized and
made available, while classifying ever-increasing numbers
of samples from the new expeditions. This unwieldy task
was done well under their direction and with the support
of NASA headquarters.
3.2.4. Storage
Once thawed during initial processing (see above), the
samples at JSC are bagged in nylon or Teflon bags and
are stored in several different types of cabinets.
Achondrites, carbonaceous chondrites, and special ordi-
nary chondrites are stored in GN2 cabinets (Figure 3.1).
The remaining samples (mostly EOCs) are stored in three
different settings: large (>500 g) samples are stored in
large-volume GN2 cabinets (Figure 3.1, a), medium-sized
(200-500 g) samples are stored in two large GN2 cabinets
with multiple trays (Figure 3.1, b), and small samples
(<200 g) are stored in stainless steel cabinets with no
nitrogen flow. Some exceptionally large samples are triple
bagged and stored on open shelves in the lab. One excep-
tional sample is LEW 85320 (Plate 2), collected in the
Lewis Cliffs Ice Tongue in 1985; because of its large size
(110 kg), a customized GN2 plexiglass storage box was
constructed and it resides in the meteorite lab at JSC. In
the event of a hurricane threat, all GN2 cabinets that
store the non-EOC meteorite samples are moved to a
watertight vault in the lunar sample facility (B31N).
3.2.5.1. Special samples.
The special list was created to
protect very unusual, scientifically unique and important
samples. Requests for these samples must be evaluated by
MWG and approved by MSG. This list is reassessed at
every MWG meeting and has changed over the years.
Some samples added to the list many years ago may have
been removed as the collection has been augmented with
similar samples. Some samples have moved onto the list
as their remaining mass has become much smaller than
