Geology Reference
In-Depth Information
CO3 chondrite
181.3 g
Found January 7, 1978
4.5 × 4.0 × 5.0 cm
Weathering = Ae
The Co chondrites contain abundant (35%-45%) but small (150
micron) chondrules and mostly Type ii metal-rich chondrules. CAis
and AoAs are present but not abundant (10%). The volume of matrix
material is low, with secondary alteration minerals including nepheline,
sodalite, fayalite, hedenbergite, and andradite, but no phyllosilicates.
There is a metamorphic sequence present in Co chondrites, from
unequilibrated 3.0 to partially equilibrate 3.7.
10
2
Acfer 094
ALHA 77307
Yamalo 81025
NWA 530
Bishunpur
Semarkona
Tagish Lake
O chondrites
Semarkona
10
-2
low FeO
high FeO
5
Julesburg (cores) +
6
5
4
3
Group 1
0
2
Group 2
TF
-5
High Z
10
-3
C chondrites
7
6
5
ALHA77307
Group 4
<1
4-44
-10
Solar
Allende (a)
4
3
<3
26-40
Allende (b)
Group 3
2-5
-15
2
Allende (c)
<1
10-14
Orgueil
CCAM
Low Z
10
-4
10
-4
0.5-4
8-25
-20
10
-3
10
-2
234567
234567
2
-15
-10
-5
0
5
10
15
18
O/
16
O
δ
18
O‰
SMOW
Plate 15
MiNERALogy
SigNiFiCANCE
ALH A77307 shows a closely-packed aggregate of min-
eral grains (up to 0.2 mm), mineral aggregates (up to
0.8 mm), and rather sparse small (0.1-0.5 mm) chon-
drules, set in a dark brown to black opaque matrix. The
matrix makes up 40%-50% of the section, and the min-
eral grains, aggregates, and chondrules consist of olivine
and polysynthetically twinned clinopyroxene in approxi-
mately equal amounts. Most of the olivine is Fa
~1
, with a
few grains ranging up to Fa
30
. Scattered grains of (1%-
2%) iron-nickel and sulfide are present in the matrix.
ALH A77307 is one of the least metamorphosed of the
Co chondrites (type 3.05; [79]), and has been an integral
sample in understanding the variation of oxygen isotopic
values in chondritic components (chondrules, matrix,
inclusions; left, [86]), as well as for identifying presolar
grains. The latter include diamond, SiC, silicates, and
oxides and are believed to come from red giant branch
(RgB) stars, asymptotic giant branch (AgB) stars, stars
with higher-than solar metallicity, or a few even of super-
nova origin (right, [92]).
References [72-94]
