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PRECIOUS STONES.
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1251
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ing,
not a piece of sandstone, quartzite, shale, or other nonigneous rock
having been observed, so far as the authors know, during the extensive
diggings. In South Africa, on the other hand, as is well known, such
foreign material is abundant in the "blue ground," and includes
quartzite, sandstone, shale, diabase, eclogite, and other rocks.
Such
fresh peridotite as occurs at the Pike County locality does not seem to
have been observed in South Africa, but the green earth of the former
much resembles the blue ground of the latter, both in color and in
being composed predominantly of highly serpentinized olivine, with
smaller amounts of decomposed augite, and a little biotite, perofskite,
and magnetite, although the Arkansas material is much softer than is
the African. Similarly, at both localities the upper portions of the
decomposed rock are yellow, through oxidation and hydration of the
ferrous iron.
On
the other hand, garnets, which are very abundant at the African pipes,
are extremely rare and of very small size at Murfreesboro, though of
the same red color, but their chemical composition is unknown as yet.
Furthermore, chrome-diopside, hypersthene, zircon, kyanite, chromite,
and ilmenite, which are such common ingredients of the African blue
ground, are unknown at the Arkansas locality. While the blue ground of
Kimberley is compact, and must be exposed for a long time to the
weather before it disintegrates sufficiently to permit the extraction
of the diamonds, the Arkansas green earth is soft and friable when
first excavated, hardens somewhat on drying, but on exposure to the
weather soon disintegrates to a fine mud, as it readily does on
agitation with water. This, at least, is true of the upper portions,
so far as they have been penetrated, but the harder fragmental material
of the first stage of decomposition shows much less tendency to
disintegrate and remains to be further investigated.
The
question of the origin of the diamonds falls outside of the scope of
this preliminary paper, but it may be noted here that no carbonaceous
shales are known to occur in the vicinity of the igneous mass, nor were
they observed as inclusions, as they are at Kimberley. This would
indicate that Lewis's view of the derivation of diamonds by the
metamorphism of carbonaceous shales does not apply here, and points to
the probable truth of the view of Cohen, Hatch, and Cor-storphine, that
they are original constituents of the igneous rock. At the same time,
in view of the occurrence of deposits of asphalt at Pike City, 10 miles
northeast of Murfreesboro, and of the occurrence in the post-Tertiary
conglomerate immediately north of Murfreesboro of some asphalt which
may be supposed to be derived from underlying organic material, the
question must, for the present, be left open.
BRIEF BIBLIOGRAPHY OF PRECIOUS STONES.
AMERICAN REFERENCES.
Baskerville, Charles. Kunzite, a new gem: Science, new ser., vol. 18, No. 304,
1903, pp. 303-304. Claremont, Leopold. Cutting and polishing of precious stones: Mineral Industry,
vol. 8, New York, 1900, pp. 229-233. Dana, E. S. On emerald-green spodumene from Alexander County, N. C.: Am.
Jour. Sci., 3d ser., vol. 22, 1881, p. 179. Ford, W. C. Some interesting beryl crystals and their associations: Am. Jour. Sci.,
4th ser., vol. 22, 1906, pp. 217-223. Johnson, Douglas Wilson. Turquoise; in The Geology of the Cerrillos Hills:
School of Mines Quart., vol. 24, 1902-3, pp. 493-499.
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