Inclusions of Hydrocarbon Fluids in Diamonds From Wafangdian, Liaoning, China

Abstract:

We studied a large number of industrial-grade diamonds from Pipe 50 of Liaoning, China. These diamonds are not suitable for polishing into gems or making cutting tools. They are usually crushed to form abrasives, without much scientific scrutiny. We report here fluid inclusions in dozens of diamonds.

The first type of fluids occur in the outer rim of diamonds, just below the surface, while their interior is free of visible fluids. Under UV radiation, when a non-fluorescent diamond appeared dim, bubbles of included fluids became visible as yellow and blue spherules. Such diamonds are sometimes encrusted with euhedral micro-diamonds resembling those on thin films grown by CVD. The second type of fluid-rich diamonds display iridescence of pink, blue, green and yellow colors. They show lamellar, filamentous, or tubular structures, some of the tubes are filled with granules, probably grown from fluids in the tubes. An FT-IR investigation of both types yielded similar results. Apart from absorption due to intrinsic diamond lattice vibrations, we found an outstanding group of bands just below wavenumber 3000. This indicates the presence of a saturated aliphatic hydrocarbons of long chain length. Our results seem to implicate that hydrocarbons might be an important component in Earth's mantle, which might even have provided carbon from which diamonds crystllized.