Ch. 3: Precious Gem stones in 1886

Page of 19

Text size:



	600 MINERAL RESOURCES.

	phosed by the peridotite, a fact which was most patent in the enveloped fragments of shale, which in one locality were quite numerous. He says that both forms of peridotite described by Professor Lewis occur in.Kentucky, but the brecciated form has not yet been found to contain diamonds. In the advanced stages of metamorphosis little spheroidal bodies were found, pale yellowish to colorless translucent to transparent, and remarkably uniform in size. These generally appeared in a form very suggestive of the diamond, resembling a hexoctahedron with curved faces. Notwithstanding that some of their properties favored the view that they were diamonds more or less perfectly crystallized, their solubility in concentrated hydrochloric acid rendered such a view untenable, and even if they were diamonds their value would be comparatively insignificant because of their small size. In concluding, he says: "The dark shale, which is frequently enveloped by the peridotite, is somewhat carbonaceous, but contains a small proportion of carbon as com pared with that of the South African diamond field. II. Carvill Lewis (Science, viii, p. 346) remarks concerning the South African mines, that" recent excavations have shown that large quantities of this shale surround the mines, and that they are so highly carbonaceous as to be combustible, smouldering for long periods when accidentally fired.'' In the chemical laboratory of the United States Geological Survey Mr. J. Edward Whitfield determined 37.521 per cent, of carbon in the shale from near the Kimberley mine, while the blackest shale adjoining the peridotite near Charles Isoin's in Kentucky, he found to contain only 0.681 per cent, of carbon. For this reason it appears to me rather improbable that diamonds will be discovered at the locality in question." Nevertheless, upon the invitation of Prof. J. li. Proctor, State Geologist of Kentucky, Mr. J. S. Diller and the writer were sent by the United States Geological Survey to examine the locality, viz: Isonvs creek, Elliott county, Kentucky. The plan was to search by sifting and carefully panning the stream beds receiving the drainage directly from the surface of the peridotite. The peridotite alters and disintegrates readily; but, from the fact that the declivity of the surface is considerable, the transportation of material almost keeps pace with disintegration, and there is no great accumulation of residuary deposits upon the narrow divides and hillsides. The specific gravity and durability of the gems found in connection with peridotite are generally greater than those of serpentine and other products of its alteration. On this account the gems accumulate upon the surface and in favorable positions along adjacent lines of drainage. We enlisted the services of the people in the neighborhood to scrutinize the steep slopes, where gems weathered out of the peridotite might be exposed. Particular attention was directed also to the examination of the solid rock and residuary deposits, which so closely resemble the material of the South African mines.

Page of 19