third the age of Earth. Nevertheless, the mass fraction of diamond observed in carburanium is several orders of magnitude smaller than that of carbonado. This presents a serious difficulty if a radiation process is to account for carbonado formation. Mass transport problems must b e . addressed; because <20% of the volume of carbonado is not diamond, some transport mechanism would have to concentrate diamond grains into large aggregates while removing the displaced uranium oxides and decay products. Because carburanium contains 500-nm polycrystalline aggregates, a sintering mechanism would then be required to coalesce these radiationformed aggregates into the micrometersized single crystal grains typical of carbonado. These factors indicate that a radiation mechanism alone cannot satisfactorily explain the formation of carbonado.
REFERENCES AND NOTES1 . V. T. Dubinchuk, A. V. Kochenov. V. F. Penkov. G. A. 994). 7. Carburanium occurs as brittle, hygroscopic oval inclusions (1 to 3 cm, p = 1.6 g/cm3) within pegmatitic veins 8 to 15 m thick (composed primarily of coarse-grained olivine and quartz) situated among gray gneisses. Carburanium sometimes replaces uranitite crystals or forms a crust on their surface. 8. Fragments with a starting mass of 3.3 g were treated with HNO, plus HCI at 20' and 40°C, &Cr, O, at 80eC, HCIO, at 140" and 220% and HCI at W°C, producing -1 mg of white residue. 9. The polycrystalline aggregates were >95 atomic % C with trace amounts of Si, 0 , Fe, Al, Mg, and Ti. The yttrium phosphate crystals exhibited trace amounts of Dy. Er, Gd, and Yb. Carburanium is usually associated with rare-earth minerals such as zirtolite. xenotime, monazite, and uraninite. 10. M. FrenWach et al., J. Appl. Phys. 66,395 (1 989).
The first broad program of scientific shallow drilling on the U.S. Atlantic continental shelf has delineated rocks of Pleistocene to Late Cretaceous age, including phosphoritic Miocene strata, widespread Eocene carbonate deposits that serve as reflective seismic markers, and several regional unconformities. Two sites, off Maryland and New Jersey, showed light hydrocarbon gases having affinity to mature petroleum. Pore fluid studies showed that relatively fresh to brackish water occurs beneath much of the Atlantic continental shelf, whereas increases in salinity off Georgla and beneath the Florida-Hatteras slope suggest buried evaporitic strata. The sediment cores showed engineering properties that range from good foundation strength to a potential for severe loss of strength through interaction between sediments and man-made structures.
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