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SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
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The Buell Park pipe now forms a basin underlain
largely by kimberlite tuff breccia (Schmitt, Swann,
and Smith, 1974). A ring-dike of olivine-bearing
minette forms a ridge, known as Peridot Ridge,
that curves across the southeast quadrant of the
basin. It was from ant hills on the slopes of this
ridge that the samples were collected for this study.
Garnet-bearing xenoliths are rare and no eclogite
xenoliths have been found (Schmitt, Swann, and
Smith, 1974).
Of a total of 227 xenocrysts analyzed for Ca, Mg,
and Cr, complete analyses were made of 179. Com-
FIGURE 5.—Ca-Mg-Fe diagram.
X garnets from Garnet Ridge A garnet inclusions in diamond
FE
plete analyses for 37 of these are given in Table 4
to show the compositional range found in Buell
Park garnets. The highest chromium content (5.1%
Cr2O3) was found in xenocryst having a pink
color. Thirty lilac color grains gave chromium contents
ranging from 1.4% to 2.6%. All of the partial
analyses are plotted on the Ca-Cr diagram, and the
complete analyses are plotted on the ternary diagrams
(Figures 7-9).
Garnet xenocrysts of varying color are present
in kimberlite tuff matrix, and they have the same
mixed origin as the detrital grains in the soil.