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SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES<br />
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Ridge and Green Knobs a few xenocrysts with between<br />
1% and 2% calcium and very low chromium<br />
are high in ferrous iron and are almandines derived<br />
from basement igneous or metamorphic rocks.<br />
At Garnet Ridge a few scattered points to the<br />
left of the garnet peridotites trend approach in<br />
composition the low calcium-high chromium content<br />
characteristic of diamond inclusion garnets.<br />
None fall well within the diamond inclusion field,<br />
however, and it is not possible to say that they have<br />
FIGURE 11.—Ca-Mg-Cr diagram.<br />
X garnets from Green Knobs A garnet inclusions in diamond<br />
CR<br />
a deeper origin than the common garnet peridotite<br />
garnet.<br />
Figure 13 is a Ca-Mg-Fe plot of garnets from<br />
three rock groups: (1) eclogite xenoliths from Garnet<br />
Ridge, (2) metamorphic rocks from Garnet<br />
Ridge, and (3) garnet peridotite xenoliths from<br />
South Africa kimberlites. The analyses are given<br />
in Tables 3 and 8.<br />
Comparison of Figure 13 with the Ca-Mg-Fe<br />
plots of garnet xenocrysts from Garnet Ridge, Buell
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