Rare-earth element patterns and carbon isotopic composition of carbonados: implications for their crustal origin.

Abstract

Carbon isotopic ratios and rare-earth element (REE) contents were measured for six Central African carbonados and two Brazilian ones. The 813C values of all the Central African samples and one of the Brazilian samples are from -29.7%o to -24.4%o, which are within the range of organic matters such as petroleum and coal, and are much lower than the typical values for ordinary diamonds of around -5961o. Another Brazilian sample gives diamond-like 813C value of -8.8%o, suggesting that this is actually not a carbonado but an aggregate of ordinary diamond such as bort and ballas. Samples with a larger amount of impurities show higher REE contents and higher light-REE/heavy-REE ratios, implying the existence of a light-REE-enriched mineral, such as florencite, along grain boundaries between diamond crystals. Chondrite normalized REE abundance patterns of the samples are similar to crustal materials such as shales rather than to kimberlites and ordinary diamonds, which are much more light-REE enriched than most of the studied samples. The Brazilian sample with a higher 813C value, however, shows a kimberlite-like REE pattern which is clearly different from that of the other Brazilian sample. From our data, the crustal origin of carbonado is preferable to its genesis in the mantle.

Hydrogen isotope compositions in carbonado diamond: constraints on terrestrial formation

“…The carbonado samples had bulk δ 13 C values of -32.0 to -24.3‰, which compositions fall in the range of previous investigations (Vinogradov et al 1966;Galimov et al 1985;Ozima et al 1991;Kamioka et al 1996;Shelkov et al 1997;De et al 2001;Kagi et al 2007;Yokochi et al 2008), indicating that the studied samples are typical of carbonado. Amorphous carbon ) with different C isotope composition from the bulk might be present in carbonado.…”

Isolation and Structural Proof of the Large Diamond Molecule, Cyclohexamantane (C26H30)

“…Interestingly, there are microcrystalline black diamonds known as carbonados, which unlike other diamonds, are believed to be formed in the Earth's crust, based on mineral inclusions. [25] The origin of these diamonds is enigmatic not only because of their crustal origin, but also their highly unusual 12 C/ 13 C isotopic ratios. Unlike other naturally occurring diamonds, which have isotopic signatures representative of mantle-derived carbon, carbonados have d…”

“…Spectra were recorded using C 6 D 6 as solvent. In the 1 H NMR spectrum, "X" corresponds to impurities; the approved IUPAC numbering for cyclohexamantane is shown, namely, dodecacyclo-[12.12.0 2,11 .0 3,16 .0 5,18 .0 6,11 .0 7,20 .0 9,22 .0 10,25 …”

Vacancy-impurity centers in diamond: perspectives of synthesis and applications

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