Geology Reference
In-Depth Information
CK5 chondrite
1040.95 g
Found December 19, 1992
13.6 × 11.2 × 4.7 cm
Weathering = A/Be
CKs are the only carbonaceous chondrite group to exhibit evidence for
widespread thermal metamorphism. CK chondrites are perhaps the most
oxidized meteorite group among the chondrites exhibiting values of fo
2
higher than FMQ. Their lack of metal and higher forsterite-content oliv-
ines suggest that they have been oxidized beyond any other group, and
their oxide and sulfide mineralogy suggests that they equilibrated at tem-
peratures close to 600 °C. Shock features in the olivine include small inclu-
sions thought to cause darkening; this may aid in identifying the parent
asteroid(s) for these chondrites.
100
E chondrites
Magnetite
90
H
80
L
CK chondrites
Ilmenite
LL
Oxidation
(metal present)
70
Oxidation
(metal absent)
60
R
50
-10
-8
-6 -4 -2
Relative oxygen fugacity (
∆
FMQ)
0
2
4
6
×900
20
µ
m
EET90007
Plate 20
MiNERALogy
SigNiFiCANCE
EET 90007 shows an aggregate of small (average about
0.02 mm) olivine grains and minor opaque material which
is mainly magnetite with a little troilite and pentlandite.
occasional chondrules, up to 1.2 mm across, are present.
olivine composition is Fa
29
; minor plagioclase of variable
composition, An
33-45
, minor diopside, Wo
40
Fs
11
.
As with other groups, CK chondrites were a small group
of samples in 1994 but have rapidly expanded into >100
samples with some diversity of mineralogy, with Antarctic
members of the group being influential in defining the
group. Detailed studies of shock features, bulk composi-
tion, and opaque minerals (sulfide, oxides; right, [122])
have allowed quantification of degree of oxidation (left,
[122]) and metamorphism compared to other groups such
as H, L, LL, and R chondrites.
References [117-125]
