Geoscience Reference
In-Depth Information
Table 3.1
Compositions of chondrites (wt.%)
Ordinary
Carbonaceous
Enstatite
H
L
CI
CM
CO
CV
Si
16.47--20.48
17.08
18.67
10.40
12.96
15.75
15.46
Ti
0.03--0.04
0.06
0.07
0.04
0.06
0.10
0.09
Al
0.77--1.06
1.22
1.27
0.84
1.17
1.41
1.44
Cr
0.24--0.23
0.29
0.31
0.23
0.29
0.36
0.35
Fe
33.15--22.17
27.81
21.64
18.67
21.56
25.82
24.28
Mn
0.19--0.12
0.26
0.27
0.17
0.16
0.16
0.16
Mg
10.40--13.84
14.10
15.01
9.60
11.72
14.52
14.13
Ca
1.19--0.96
1.26
1.36
1.01
1.32
1.57
1.57
Na
0.75--0.67
0.64
0.70
0.55
0.42
0.46
0.38
K
0.09--0.05
0.08
0.09
0.05
0.06
0.10
0.03
P
0.30--0.15
0.15
0.15
0.14
0.13
0.11
0.13
Ni
1.83--1.29
1.64
1.10
1.03
1.25
1.41
1.33
Co
0.08--0.09
0.09
0.06
0.05
0.06
0.08
0.08
S
5.78--3.19
1.91
2.19
5.92
3.38
2.01
2.14
H
0.13
—
—
2.08
1.42
0.09
0.38
C
0.43--0.84
—
—
3.61
2.30
0.31
1.08
Fe
0
Fe
tot
0.70--0.75
0.60
0.29
0.00
0.00
0.09
0.11
/
Mason (1962).
similar to that of the sun. The volatile-rich car-
bonaceous chondrites are samples of slightly
altered, ancient planetesimal material that con-
densed at moderate to low temperatures in the
solar nebula. The nonchondritic meteorites are
differentiated
materials of nonsolar composition
that have undergone chemical processing like
that which has affected all known terrestrial and
lunar rocks.
Meteorites are assigned to three main categor-
ies. Irons (or siderites) consist primarily of metal;
stones (or aerolites) consist of silicates with little
metal; stony irons (or siderolites) contain abun-
dant metal and silicates.
since their formation; that is, they have not been
buried deep inside planetary objects.
The CI or Cl meteorites are the most extreme
in their primordial characteristics and are used
to supplement solar values in the estimation of
cosmic composition. The other categories of car-
bonaceous chondrites, CII (CM) and CIII (CO and
CV), are less volatile-rich.
Some carbonaceous chondrites contain
calcium--aluminum-rich inclusions (CAI), which
appear to be high-temperature condensates from
the solar nebula. Theoretical calculations show
that compounds rich in Ca, Al and Ti are among
the first to condense in a cooling solar nebula.
Highly refractory elements are strongly enriched
in the CAI compared to Cl meteorites, but they
occur in Cl, or cosmic, ratios.
Cl 'chondrites' are fine grained, do not con-
tain chondrules and are chemically similar, to
the true chondrites (see Table 3.1).
As the name suggests,
ordinary chondrites
are
more abundant, at least in Earth-crossing orbits,
than all other types of meteorites. They are chem-
ically similar but differ in their contents of iron
Carbonaceous chondrites
Carbonaceous chondrites contain high abun-
dances of volatile components such as water and
organic compounds, have low densities, and con-
tain the heavier elements in nearly solar pro-
portions. They also contain carbon and mag-
netite. These characteristics show that they have
not been strongly heated, compressed or altered
