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Antarctica - Part 5a

Smithsonian Contributions to the Earth Sciences, Number 23

Catalog of Antarctic Meteorites, 1977-1978

Initial Processing and Description

Each individual bag containing one or several meteorites, was
transferred from the cold storage room to the processing laboratory in
the JSC Curatorial Facility, was placed inside a chilled stainless steel
can on a laminar flow bench, and was opened. A meteorite was withdrawn
and compared to its field photograph to confirm its field
identification. The meteorite was then placed inside a clean teflon bag
inside a second chilled can, a processing identification number was
assigned, and the meteorite was returned to the freezer. This process
was repeated for all specimens. It was possible to identify many
meteorites with their field photographs and to determine their
orientation on the ice. Processing numbers initially assigned to the
specimens were 30001 to 30307. These were later replaced by the
permanent name/number combinations recommended by the Committee on
Nomenclature of the Meteoritical Society. For all of the 1977-1978
collection, except one meteorite, these carry the information of
locality, Allan Hills (ALH); field party (A); field season (77);
followed by a three-digit number which identifies each individual
specimen collected. The sequence in which these last three digits were
assigned was based on the order of unpackaging in Houston, not on the
order of recovery in Antarctica. Thus, when referred to in the catalog,
the first specimen in the collection bears the identification:
ALHA77001, xx, where the digits following the comma refer to subsamples
taken from this meteorite specimen. The initial processing of meteorites
in the Curatorial Facility provided a rapid characterization of each
specimen that was reported to the meteoritical community via the
Antarctic Meteorite Newsletter, which was created for this purpose.
Each meteorite was weighed, photographed, described, and a small chip
was taken for a thin section. In most cases the chip was sent to the
Division of Meteorites at the Smithsonian Institution (SI), where thin
sections were made and the meteorites classified petrographically. The
processing was done in a cleaned, stainless steel glove box with a
controlled nitrogen atmosphere, using cleaned tools generally limited to
stainless steel, aluminum, and teflon. The tools and techniques used
were those routinely used for processing lunar samples, except that
techniques were modified for greater efficiency wherever it was
considered appropriate. The intent was to prevent any serious
contamination or degradation of the specimens during initial processing.
Attempts were made to keep many meteorites cold throughout these
operations. For example, photographs were taken while the meteorite lay
on a specially prepared stage, which was kept chilled by directing a
small stream of liquid nitrogen onto its underside. The meteorite was
always returned to this cold plate between operations, such as weighing
and chipping. For many of the larger specimens, a chip was taken to be
kept in long-term cold storage after the main mass of the specimen had
been warmed. A summary of the initial processing steps in their
approximate order is as follows:
With specimen kept cold, (1) each meteorite was quickly passed into the
processing cabinet, removed from its bag and placed on a cold plate; (2)
weighed; (3) photographed in color (orthogonals were taken of larger
specimens); (4) a chip was taken for thin sections; (5) a second chip
was taken (from the larger specimens only) for long-term cold storage;
and (6) the specimen was dried (a few were freeze-dried but most
meteorites were allowed to thaw in the nitrogen cabinet). After thawing,
(7) each specimen was sawed in half and the cut surfaces photographed
and described; (8) one-half of each meteorite was sent to Japan along
with one of three thin sections made at the Smithsonian Institution. The
two other thin sections were placed in libraries at the JSC Curatorial
Facility in Houston and at the SI Division of Meteorites in Washington,
where scientists may examine them.


Best regards,

Bernd

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