Geology Reference
In-Depth Information
EL3 enstatite chondrite
74.4 g
Found January 14, 1989
4.0 × 4.0 × 2.5 cm
Weathering = A
our meteorite collections and are composed of nearly pure Mg end-
member silicate minerals such as enstatite and metallic FeNi metal that
contains Si. EL chondrites also 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, Moon, and aubrites.
FeS
Niningerites and
Alabandites
(mol. %)
Ta e
Tr
Isotherms from Skinner
and Luce (1972)
Ka
Tr
Per
50
Ala
Sch
LEW
87223
EH4-5
EL6
EH3
EL3
MnS
MgS
50
3
20 KV
30
µ
m
17, 000
Plate 31
MiNERALogy
SigNiFiCANCE
MAC 88136 contains abundant chondrules and chon-
drule fragments, ranging up to 2.4 mm diameter; they
consist of granular or cryptocrystalline pyroxene. The
matrix consists largely of small pyroxene grains, with
some nickel-iron metal and minor sulfides. one ellipsoid
metal grain, 1.1 × 1.5 mm, is present in the section.
Microprobe analyses show that the pyroxene is clinoen-
statite, with variable but low iron content (Feo 0.1%-
2.1%); the metal grains show a low and variable silicon
content, ranging up to 0.5%.
MAC 88136 was the first known primitive (EL3) chon-
drite; prior to its discovery, only highly metamorphosed
examples of EL chondrites were known. The MAC 88136
enstatite chondrite contains accessory olivine particu-
larly rich in chromium. During metamorphism, chro-
mium diffuses out of olivine. With Cr
2
o
3
concentrations
up to 0.6 wt.%, MAC 88136 contains the most chromium-
rich olivines found in enstatite chondrites, perhaps indi-
cating that it is one of the most primitive members of the
enstatite chondrite group. Perryite, (Ni,Fe)
5
(Si,P)
2
, and
alabandite, (Mn, Fe,Mg)S, are among the unusual opaque
minerals found in MAC 88136 (left [220] and right [213]).
References [205-220]
