Geology Reference
In-Depth Information
EH3 enstatite chondrite
2.63 g
Found January 20, 1982
2.0 × 1.1 × 0.5 cm
Weathering = C
our meteorite collections, and are composed of nearly pure Mg end-mem-
ber silicate minerals such as enstatite and metallic FeNi metal that contains
Si. EH chondrites include petrologic types 3 through 6, with unequilibrated
type 3 chondrites providing insight into nebular processes in a more
reduced portion of the solar nebula. Enstatite chondrites also share the
same oxygen isotopic signature as the Earth, the Moon, and aubrites.
Ti (wt%) in troilite
(A) ALHA81189
30
15
(B) Sahara97096
30
15
Group 1
(C) ALH84170
30
ALHA81189
Ya mato-691
Solar
30
15
10
8
(D) St. Marks
6
Detection
limit
30
4
15
Group 4
2
σ
2
1.6
2.0
18
O/
16
O (×10
-3
)
2.4
2.8
0.0
0.25
Ti (wt%)
0.5
Plate 29
MiNERALogy
SigNiFiCANCE
ALH A81189 contains an aggregate of chondrules, chon-
drule fragments, and mineral grains set in an opaque
matrix. The chondrules range up to 0.9 mm in diameter;
most of them consist of granular pyroxene (sometimes
with a little olivine), but a few are made up of nickel-iron
and troilite. The matrix consists largely of nickel-iron and
troilite, with a considerable amount of limonite formed
by weathering of the metal. Microprobe analyses show
that the pyroxene is close to MgSio
3
in composition.
Most of the olivine grains are close to Mg
2
Sio
4
in
composition.
ALH A81189 may be the most primitive EH3 chondrite.
However, variations in chondrule types suggest that it is
not the metamorphic protolith of other EH3 chondrites.
ALH A81189 formed at slightly higher oxygen fugacities
than other EH3s, based on the lower Ti content of the
troilite (right, [196]). it also contains presolar grains that
record stellar processes just like a few other meteorites in
our collection (QUE 99177, QUE 97008; left, [193]).
References [193-196]
