『Abstract
The reviewer presents the results of a literature search on the
enigmatic occurrences of carbonado; a form (but not the only form)
of polycrystalline diamond, which is mined for industrial diamonds.
The principal occurrences are in Brazil, the Central African Republic
(CAR) and Siberia (Yakutia). In the latter the name yakutite has
been coined, but, though there are differences between these polycrystalline
diamonds and the Brazil/CAR minerals, they would seem to be little
more significant than differences within the ‘Gondwana’ occurrences,
and ‘yakutite’ should probably be regarded as another name for
carbonado. Most occurrences are in placers and the minerals have
probably been recycled more than once by sedimentary processes,
the ultimate source being unknown. Polycrystalline diamond has
been described from the Udachnaya pipe, Yakutia and, though it
is strictly framesite (defined as an eruptive pipe variety of
carbonado), it differs little from other carbonados. The fact
that all occurrences known are in areas with kimberlites and gem
diamond developments present, suggests that carbonado does stem
from terrestrial eruptive processes, though not necessarily kimberlite
pipes. Nevertheless, this can be only a provisional, personal
conclusion, there is much contradictory evidence in the literature.
The evidence of subjection to radiogenic agencies in CAR carbonados
seems to be unexplained, but it may be a secondary effect and
not present in all carbonados. This is a conundrum which still
calls for much more research.
Keywords: carbonado; polycrystalline diamond; placers; diamond
pipes; industrial diamonds; impact; polycrystalline; kimberlite
pipes; carbon isotopes』
Contents
1. Introduction
2. Historical
3. Possible origins suggested for carbonados
4. Brazil and the CAR
5. Siberia
6. Isotopically-light pipe diamonds
7. Discussion
8. Conclusion
References