[meteorite-list] Black Diamonds: A interesting PBS NOVA article

From: cdtucson at cox.net <cdtucson_at_meteoritecentral.com>
Date: Mon, 13 Apr 2009 22:25:41 -0700
Message-ID: <20090414012541.12JI2.585222.imail_at_fed1rmwml29>

Steve,
Forgive me if you already covered this but, Are these carbonado diamonds the same as the ones found in meteorites such as Canyon Diablo? I believe That variety are referred to as Lonsdaleites. and have a hexagonal structure. Are they also porous? Thanks
Carl Esparza
IMCA 5829

---- Steve Schoner <schoner at mybluelight.com> wrote:
> Paul,
>
> Right. And the fact that they occur only in two places on earth and are found no where else, further complicates the issue.
>
> I think that the Earth and moon were asteroid bombarded very intensely in two prolonged events. 2.9 and 3.7 billion years ago. And this leads to me really wonder about these carbonado diamonds that are so distinct from the others which were clearly formed in the Earth's upper mantle. The fact that these have an odd amorphous polycrystalline structure and are tougher than the normal terrestrial diamonds makes me wonder more about their origins, too.
>
> Steve Schoner
> IMCA 4470
>
> P.S. I noticed that these are suddenly selling on ebay from the best and till now only supplier of carbonados (aaaroughy). One must watch out though, as the term "carbonado" is a term used loosely in the diamond trade. To most legit diamond dealers all dark, brown to black diamonds are "carbonado." The distinction for a true carbonado is its porous structure which is clearly evident to the eye either directly or under magnification.
>
>
> ------------------------------
>
> Message: 10
> Date: Sun, 12 Apr 2009 19:23:49 -0700 (PDT)
> From: Paul <bristolia at yahoo.com>
> Subject: [meteorite-list] Black Diamonds: A interesting PBS NOVA
> article
> To: meteorite-list at meteoritecentral.com
> Message-ID: <757237.64780.qm at web36206.mail.mud.yahoo.com>
> Content-Type: text/plain; charset=utf-8
>
>
> Personally, I do not know what to think about the
> origin of carbonados. I do think that "there is much
> contradictory evidence in the literature" and "This
> is conundrum which still calls for much more research."
> to quote from the abstract of:
>
> McCall, G.J.H., 2009, The carbonado diamond conundrum.
> Earth-Science Reviews. vol. 93, no. 3-4, pp. 85-91.
> http://dx.doi.org/10.1016/j.earscirev.2009.01.002
>
> Whatever happened to create carbonados, happened a
> very long time ago as discussed by:
>
> Yuji, S., R. Yokochia, K. Teradab, M.L. Chaves, and
> M. Ozimad, 2002, Ion microprobe Pb-Pb dating of
> carbonado, polycrystalline diamond. Precambrian
> Research. vol. 113, no. 1-2, pp. 155-168
> http://dx.doi.org/10.1016/S0301-9268(01)00208-X
>
> Some quotes from Yuji et al. (2002).
>
> "Pb?Pb age of mineral inclusions in GM01 carbonado,
> 3.3+/-0.7 Ga is older than the formation age of the
> Sopa conglomerate in carbonado-bearing deposit
> related to the first extensional event in southeast
> border of the Sao Francisco craton at 1750?1700 Ma
> (Uhlein et al., 1998). Therefore, the carbonados
> were originated somewhere else and later incorporated
> in the Sopa conglomerate."
>
> "Mineral inclusions (rutile, florencite, quartz,
> zircon, and clay minerals) of GM01 and DO3
> carbonados are typically crustal. The upper mantle
> origin of the carbonados may be, therefore, ruled out."
>
> "In addition we can not find any evidence of high
> pressure shock-metamorphism such as occurrence
> of coesite based on the mineral assemblage of the
> carbonado inclusions. Therefore, the early impact
> origin of the carbonados is probably excluded."
>
> "207Pb/206Pb isochron age of DO3 carbonado
> matrix is consistent with that of Central African
> carbonado reported by other workers, suggesting
> a close genetic relationship between Brazilian and
> African carbonados within a united landmass
> during the Archean, as supported by 3.6 Ga zircons
> observed in the conglomerate.
>
> With the contradictory evidence for their origin,
> the lack of any carbonados being found in place where
> they formed, and their great age, it might be very
> difficult to understand exactly how they formed.
> Because of their great age and having been eroded
> and redeposited from the parent strata in which they
> either form in place or accumulated as debris from
> some extraterrestrial event means a lot of the
> critical evidence concerning their origin has been
> lost.
>
> Yours,
>
> Paul H.
>
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Received on Tue 14 Apr 2009 01:25:41 AM PDT