Geology Reference
In-Depth Information
average thickness of 1 cm, overall height of 9 cm, and width
of 15 cm. Assuming a density of 2.64 g/cm
3
(calculated for
this composition using
Ghiorso and Sack
, 1995) results in a
mass of ~360 g. This estimate does not take into account the
irregularities in the surface, such as the two visible dimples in
many images (see Meyer, Mars Meteorite Compendium at
may have some uncertainty (+/−10 g).
Two issues contribute to a major difference between
the mass that is present, and the mass that is usable. First,
the fusion crust is present over much of the exterior of
Lithology B. Most researchers do not want to study pieces
with fusion crust attached, so any piece of B that has fusion
crust adhered is generally not usable (though still kept in the
collection). Second, the contact between A and B is prob-
lematic. Not only is the contact gradational, it also has a
large area, roughly 9 cm × 15 cm. There are many pieces of
EET A79001 that were generated during subdivision that
are mixtures of both lithologies. Separating A and B on
small pieces is difficult if not impossible. To complicate the
situation further, there was originally a natural fracture
plane present at an oblique angle to the contact. During
band sawing, this fracture created many small pieces that are
a mixture of both Lithology A and B, such that the actual
usable mass of Lithology B is reduced considerably from the
estimated total mass. We can get an idea of what percentage
of material is usable (70% -75%; see below) by looking at
allocation data from a few individual pieces.
The first round of major allocations of Lithology B
occurred in 1980, when the sample was band sawed into
what became splits ,1 and ,2 and a 1-cm slab (,22). Band
sawing in a GN2 cabinet was done frequently, and the
cutting through Lithology B can be seen in Figure 3.10,
with the final slab and ,2. The second major subdivision
of Lithology B came with the band sawing of ,1 to
produce ,216 and ,1. Many allocations of Lithology B
were subsequently made from ,216 (NASA photo S86-
26478), and a substantial portion of Lithology B remains
on ,1 (NASA photo S86-26477) and well as on ,2. A sum-
mary of the subdivision of EET A79001 was prepared by
C. Meyer for the Mars Meteorite Compendium (
http://
Based on the photographic information and data packs,
we can summarize how much material from Lithology B
has been used to estimate how much of the available mass is
actually usable mass. For slab ,1 the original mass was ~24 g,
and allocated mass is 18.1 g (13.6 g chips + 4.5 g potted butt).
The remaining material from ,1 is either fine mixture of A
and B, has fusion crust attached, or is attrition, which yields a
usable mass of ~75%. Similarly, for split ,216, the original
mass was ~46 g, and allocated mass is 32.1 g (all chips). The
remaining material from ,216 is either fine mixture of A and
B, has fusion crust attached, or is attrition, which yields a
usable mass of ~70%. This number (70%-75%) can be used
as a guide for future estimates of usable remaining mass by
the curation group. For example, if 75% of the original
mass of Lithology B is usable then that leaves 270 g. So far,
0.7 g + 32.1 g + 18.1 g have been allocated. Therefore, it
seems that approximately 20% of the usable mass of
Lithology B has been allocated to scientists for study, leav-
ing about 80% or just over 200 g. Although 200 g is a rea-
sonable amount of material, it is recommended that
allocations of this sample, due to its scarceness, be limited
to studies that cannot be completed using other available
basaltic shergottites or martian meteorites.
3.3.3. QUE 94201: Small Rare Martian Meteorite
(Plate 71)
In 1994, a 12.02-g meteorite, now called QUE 94201,
was found in the Queen Alexandra Range of the
Transantarctic Mountains. This sample is a basaltic rock
(shergottite) that represents a melt of reduced and
depleted martian mantle [see
McSween et al
., 2014 (this
volume)], contains hydrous phosphates, and has been an
important sample to the Mars geoscience community. As
such, it has been in high demand, and the Meteorite
Working Group has been an important body in preserving
this sample for the most effective research use. Since 1994,
this sample has been subdivided into 63 splits, including
27 bulk samples (4.416 g) for destructive analysis, and 13
thin sections (using 2.2 g). To date, 23 principal investiga-
tors have studied the first set of splits (subsamples), and 29
principal investigators have examined splits that were cre-
ated subsequently. In addition, 5.16 g of material is still
available for study using new techniques or by a new gen-
eration of scientists. The manner in which QUE 94201
was subdivided and the number of investigators involved
provides a case study for what we might expect if small
samples like this are collected during a Mars Sample
Figure 3.10.
Band sawing of main mass (slab = ,22) of EET
A79001 (NASA photo S81-25260).
