Geology Reference
In-Depth Information
Mesosiderite
8132 g
Found December 29, 1987
25.0 × 16.0 × 12.5 cm
Weathering = B
a diverse group of meteorites. The silicate portions of mesosiderites are
very similar to eucritic and diogenitic materials, with gabbroic and basaltic
clasts as well as large orthopyroxenes. in addition, there are many addi-
tional mineral fragments and lithologies. The mesosiderite metal is similar
in composition to that in the pallasite and iiiAB iron meteorites. How-
ever, a link between mesosiderites and these other groups has not been
definitively made.
EET 87500
0
100
200
300
400
Mesosiderites
8
6
4
2
0
Pallasites
10
8
6
4
2
0
0
100
200
300
400
Cosmic-ray exposure age (m.y.)
Plate 75
MiNERALogy
SigNiFiCANCE
EET 87500 is composed of a granular aggregate of
approximately 50% pyroxene, 30% nickel-iron, and 20%
plagioclase, with accessory merrillite and an Sio
2
poly-
morph, probably tridymite. The grain size is relatively
coarse, with individual pyroxene (mean of Wo
6
Fs
30
) and
plagioclase (An
91-96
) grains up to 2 mm across. Many
pyroxenes are partly or completely converted into a
mosaic of small granules.
The mesosiderites exhibit a wide range of textures and
mineral compositions, and EET 87500 has contributed
to documenting the range of these characteristics within
the group. it also has the oldest cosmic ray exposure age
(340 Ma) of the mesosiderites (right, [807]), making it an
important sample in establishing the origin and parent
body or bodies of the mesosiderites.
References [804-807]
