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110 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
FIGURE 6.—Fine silicate texture, inclusion 5: a, transmitted light (black vein in upper left is
graphite); b, reflected light (white grains in graphite vein are metal, in silicate area troilite).
(Fe + Mg) ratio occur in olivines and pyroxenes of
different inclusions. Special care was taken, by
repeated measurements, to establish these differences
beyond doubt. Table 3 shows the results of
repeated measurements of the same grains in two
inclusions. Table 4 gives the mean FeO contents
for olivines and FeO and CaO contents for orthopyroxenes.
The spread in FeO values for a given
inclusion is shown in Figure 8.
Two results are evident from Table 3 and Figure
8: (1) The spread of FeO content found within
one and the same inclusion is small, but real, as
the values are reproducible by repeated measurements.
(2) The difference of FeO content in olivines
in different inclusions is real and reproducible. The
clearest cases are sections 5 and 10, with an average
of 4.5 ±0.2% FeO and 3.6 ±0.2% FeO respectively.
Figure 8 shows that the ranges of FeO content in
olivine in these sections do not overlap. Most
olivine compositions of the other inclusions center
around values of 4% FeO. The pyroxene average
values are also distinctly different for different
TABLE 1.—Mineral composition of silicate inclusions 1, 4, and
5, determined by point-counting in weight percent
Mineral
Orthppyroxene . . .
Clinopyraxene ...
Plagioclase ....
Sum of silicates
Graphite
Nickel-iron . . .
Iron oxide*. . . .
Itotal
Points counted
Inclusion 1
33
35
2.5
5.4
75.9
22
0.1
0.6
1.7
100.3
1300
•Formed by terrestrial weathering.
Inclusion 4
21
44
0.8
11.5
77.3
14
3.4
5.5
—
100.2
1000
Inclusion 5
43
21
2.7
7.8
74.5
0.8
16.5
4.9
3.2
99.9
1000