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 <[email protected]> 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 <[email protected]> > Subject: [meteorite-list] Black Diamonds: A interesting PBS NOVA > article > To: [email protected] > Message-ID: <[email protected]> > 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. > > ____________________________________________________________ > Click to find schools offering certificate programs. > http://thirdpartyoffers.mybluelight.com/TGL2341/fc/BLSrjpdrbsmuB68xeyVrARQiTyZ0rn2wZ9rfKyNoClWYOpqgMAL9ZaOZGNq/ > ______________________________________________ > http://www.meteoritecentral.com > Meteorite-list mailing list > [email protected] > http://six.pairlist.net/mailman/listinfo/meteorite-list ______________________________________________ http://www.meteoritecentral.com Meteorite-list mailing list [email protected] http://six.pairlist.net/mailman/listinfo/meteorite-list
