Geology Reference
In-Depth Information
Olivine diogenite
12.68 g
Found January 11, 1999
2.0 × 2.0 × 2.0 cm
Weathering = B
been recognized that contain significant (>10%) olivine in addition to the
orthopyroxene as a major silicate phase. gRA 98108 is such a sample and
is coarse grained with as much as 20% olivine.
100
Acapulcoites/lodranites
Winonaites
Brachinites
Pallasites
Diogenites
80
60
GRA 98108
40
20
0
0.5
0.6
0.7
0.8
0.9
1. 0
Molar Cr/(Cr+Al) in chromite
Plate 60
MiNERALogy
SigNiFiCANCE
gRA 98108 contains 80% orthopyroxene, nearly 20%
olivine, and minor amounts of chromite, plagioclase,
clinopyroxene, FeNi metal, troilite, and silica. The
orthopyroxene has Mg# of 0.77, olivine of Mg# = 0.73,
and plagioclase is An 91 .
gRA 98108 has one of the highest Mgo contents of dio-
genites and may represent the deeper or more primitive
part of a differentiated asteroid where olivine may have
been part of the fractionating assemblage. The Feo/Mno
ratio of gRA 98108 is like other diogenites but distinct
from other olivine-rich achondrites (above, [441]).
Because diogenites typically have a small compositional
range, and we do not have samples of the mantle of the
diogenite parent body, these olivine-rich diogenites may
provide compositional leverage that can help to better
constrain models for early differentiation.
References [439-443]
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