Geology Reference
In-Depth Information
3.2.6.3. Iron meteorite and pallasite preparation at
Smithsonian.
Iron meteorites and pallasites are stored
and processed at the Smithsonian. These meteorites,
unlike other meteorite types, are stored at the National
Museum of Natural History. The majority of these
are stored in auto-desiccators to reduce oxidation
(Figure 3.2). Sample preparation facilities are specially
equipped for cutting, polishing, and sectioning irons and
predominantly iron-bearing meteorites. Iron meteorites
and pallasites are cut using specialized composite (a
hardened rubberized compound impregnated with abra-
sives) blades. Blade composition and sources can be
provided upon request. Polished sections are made with
standard epoxy and polished with diamond paste and
aluminum oxide.
[1990], with an update published in 2006. This small
formal contribution to the program is only one example
of Gene Jarosewich's important involvement with the
Antarctic meteorite collection [e.g.,
Clarke et al.
, 2006].
3.2.7. Cleaning and Contamination
Collection and curation of Antarctic meteorites for
35 years have resulted in identification of potential con-
taminants, both organic and inorganic, to meteorite
samples. Organic matter (windblown microorganisms or
organic compounds) may be present in the ice [
Stroeven
et al.,
1998;
Burckle and Delaney
, 1999;
Botta et al.
, 2006]
in which meteorites sit for ~100 Ka, and even though
storage in nitrogen minimizes oxidation and reactivity of
samples, the environment is not totally free of organ-
isms, as anaerobic bacteria can survive in some samples
[
Fries et al.
, 2005]. Nonetheless, curation facilities can be
designed to guard against additional contamination.
There are various ways in which the environment is kept
as clean as possible, including special cleaning proce-
dures, air filtering, and monitoring for potential contam-
ination. Some of these practices changed substantially
following the 1996 announcement of evidence for pos-
sible fossil life and biochemicals in ALH 84001 [
McKay
et al
., 1996] (see also Plate 69). The increased awareness
of organic contamination of the Antarctic meteorites
prompted several changes to the Antarctic meteorite lab
at JSC: establishment of a dedicated cabinet for
processing martian meteorites, separate storage of mar-
tian meteorites and most carbonaceous (once they are
classified), and installation of a new HEPA filtered air
system (see below). In addition, organics testing took
place in clean rooms, including air samples, exposed wit-
ness plates in cabinets, and the ultrapure water (UPW)
used to clean tools and bags. The cleaning and moni-
toring approaches are discussed below.
Cleaning of cabinets, heat sealers, balances, bags, tools,
containers, and equipment used in the curatorial labs cur-
rently follows specific guidelines (
Johnson Space Center
,
2006;
Calaway et al.
, 2013a,b]. For many years, cleaning
of curatorial items was done using a Freon rinse (until
the mid-1990s). In the 1970s and 1980s, the cleaning was
done with Freon, and the cleanliness of the final flush
was checked by particle counts, nonvolatile residue
(NVR), and total hydrocarbon (THC) tests. Freon
cleaning was done using three venues but all the same
procedure: a Freon still in the high bay of Building 31,
White Sands Test Facility, and the JSC Building 9 facility.
Curatorial staff used the in-house Freon still whenever
possible, but sometimes demand became too high for the
size of the still, and at these times, White Sands or
Building 9 would provide supplemental support. When
Freon cleaning was discontinued, it was replaced with a
3.2.6.4. Thin and thick section preparation.
The mete-
orite thin section labs at JSC and the Smithsonian can
prepare standard 30-micrometer thin sections, thick sec-
tions of variable thickness (100 to 150 micrometers are
common for LA-ICP-MS or microdrilling), or demount-
able sections using superglue for use in TEM studies. At
JSC, water is not used in any part of the thin-sectioning
process; instead, light mineral oil and alcohol are used for
the cutting, grinding, and polishing stages; thin sec-
tioning at SI utilizes water unless otherwise specified.
Diamond grinding wheels are used on some samples, as
well as a SiC slurry for lapping. Polishing compounds are
typically diamond paste or diamond fluids, but alumina
can be used as a final polish as well. Pure silica slides are
available as a substitute for standard petrographic glass
slides, if necessary.
3.2.6.5. JSC and SI “library” materials (thin sections
and powders).
A library of thin sections of all non-EOC
(and some EOC) specimens is maintained at SI and JSC
(those at JSC for meteorites with original mass >10 g).
All enstatite meteorite (aubrite, EH, and EL chondrite)
thin sections are stored in electronic desiccators to avoid
breakdown of water-soluble minerals such as oldhamite.
MWG does not in general advocate the loan of SI library
sections, in order to maintain one relatively complete
library. In special cases, however, the SI library section
may be loaned for a brief period (up to 2 weeks) by the SI
curator with the consent of one other member of MWG.
The JSC library sections are not generally loaned out to
PIs for research purposes except in rare cases and for no
more than 3 months. PIs are free to visit both facilities to
examine thin sections at any time after their announce-
ment in the Antarctic Meteorite Newsletter.
For many large meteorites collected during the early
years of the ANSMET program, homogenized powders
were prepared by Gene Jarosewich and archived at the
Smithsonian. A full listing is reported in
Jarosewich
