Geology Reference
In-Depth Information
Ungrouped achondrite
4.12 g
Found December 17, 1988
2.0 × 1.6 × 0.6 cm
Weathering = B
the foundation for a new group of achondrites, once more are discovered.
However, there are several that have remained one-of-a-kind samples even
after close to 25 years in the collection. These unusual samples offer
insight into the diversity of materials in the solar system.
4
10
Eagles Nest
LEW88763
ALH 84025
Brachina
Y
D
1
ALH
EN
2
R
H
B
0.1
Brachinites
Other Olivine-Rich
Aubrites
Ureilites
Winonaites/IAB Silicates
Acapulcoites/Lodranites
Pallasites
0
LEW
0.01
Al
Sc Ca
VMgFeCrMnKNa Ga Br Se Zn
2
4
6
8
δ
18
O
Plate 43
MiNERALogy
SigNFiCANCE
LEW 88763 is a fine-grained (<1 mm crystals), granular
textured, olivine-rich (70% Fo
63
) rock with minor plagio-
clase (Ab
55-76
An
44-19
or
2-7
), augite, pigeonite, chromite,
whitlockite, ilmenite, trolite, and taenite.
Although initially thought to be a brachinite, an achon-
drite group that formed by igneous processes on a differ-
entiated body, it has distinct oxygen isotope and bulk
compositional characteristics (left and right, [290]).
instead, its similarity in bulk composition to chondritic
meteorites suggests that it may represent material that has
been heated and recrystallized, perhaps even lost a very
small portion of sulfide to a melting event. This sample
lies at the boundary between chondritic and achondritic
meteorites and may provide important distinctions bet-
ween these groups as more such samples are found.
References [286-290]