[Rockhounds] Diamond clues to beasts' demise

Tue Jan 6 17:06:25 PST 2009

Thanks, Pete, for doing this research.

So does anybody know what the n-diamond polymorph is?  I didn't!
I did a bit of web searching using "n-diamond polymorph".  Got more  
than I want to try to understand!  But here is an abstract from a  
recent presentation at  American Geophysical Union (Dec. 2008),  
probably already referred to in this thread and definitely related to  
the Science article that Pete M. quotes below, since the list of  
authors is basically the same, but scrambled around:

American Geophysical Union, San Francisco, CA December 15 and 19, 2008
Younger Dryas Boundary Impact Abstracts

Oral Presentations (Tuesday, December 16)

1) Presence of all Three Allotropes of Impact-Diamonds in the Younger  
Dryas Onset
Layer (YDB) Across N America and NW Europe

West, A.a, Kennett, J. P.b, Kennett, D. J.c, Que Hee, S. S.d,  
Wolbach, W. S.e, Stich, A.e,
Bunch, T. E. f, Wittke, J. H. f, Mercer, C. g, Sellers, M.h,  
Culleton, B. J. c, Erlandson, J.
M.i, Johnson, J. R. j, Stafford, T. W., Jr.k, Weaver, J. C. l, West,  
G. J.m

We report the discovery of all three diamond allotropes (cubic  
diamond, lonsdaleite, and
n-diamond) in an extraterrestrial (ET) impact layer (the YDB), dating  
to the Younger
Dryas onset at 12.9 ka. YDB diamonds are distributed broadly across N  
America and NW
Europe at 15 sites spanning 9,000 km or 23 percent of Earth‟s  
circumference. N-
diamonds and lonsdaleite, or hexagonal diamond, do not co-occur with  
terrestrial
diamonds, but are found in meteorites. Lonsdaleite is found on Earth  
only in association
with known ET impacts, and thus, is a definitive impact indicator.

Interestingly enough, the Science article only references cubic  
diamond and n-diamond in the abstract (I could not look further  
without $$$), and does not mention hexagonal diamonds (or  
lonsdaleite) at all.  But the abstract above clearly identifies  
hexagonal diamonds as being the same as lonsdaleite.

So perhaps the reference to hexagonal diamonds came from this earlier  
AGU abstract and got picked up as easier to describe to the public  
than lonsdaleite and n-diamonds, and then the authors chickened out  
about lonsdaleite?  And so perhaps the reference is now moot?

Pete Richards

On Jan 6, 2009, at 6:47 PM, pmodreski at aol.com wrote:

> A P.S. to the 13,000 b.p. impact-produced diamonds discussion,
>
> After reading all these posts (or at least most of them) about this  
> topic, I found I was able to go through our USGS library online and  
> read the original article in the journal, Science, about it (2 Jan  
> 2009, vol. 323; "Nanodiamonds in the Younger Dryas Boundary  
> Sediment Layer" and, even better, the "News of the Week-Planetary  
> Impacts" story from that issue of Science, "Did the Mammoth Slayer  
> Leave a Diamond Calling Card", which described the background for  
> this research (and which is much more readable).
>
> It seems that our Rockhounds discussion got onto somewhat of a side  
> track about whether "hexagonal diamonds are still diamonds".  Nice  
> discussion, but, though the BBC story did use these terms, unless I  
> am missing it, the actual Science article by D.J. Kennett et al.  
> never mentions lonsdaleite, nor anything about "hexagonal".  It  
> refers to them as "nanodiamonds", also as "the n-diamond  
> polymorph", which crystallizes "under lower temperature-pressure  
> conditions".  They also refer to recovery of "typical cubic  
> diamonds" from one site (Bull Creek, Oklahoma), and describe  
> "subrounded, spherical, and octahedral crystallites, ranging in  
> size from 2 to 300 nm, distributed within carbon spherules", and  
> refer to electron diffraction patterns producing "d-spacings  
> typical of cubic diamonds" as well as "additional 'forbidden'  
> reflections consistent with the n-diamond polymorph".
> 0D
> The News of the Week" story notes that other researchers have still  
> questioned the interpretation of this data, and some groups have  
> reported carbon spherules and nanodiamonds from other soil horizons  
> of various ages, questioning whether there is really any  
> correlation with an impact event or events.  [maybe they are just  
> generic cosmic dust filtering down to Earth??--my comment, not theirs]
>
> and, a P.P.S. to this, I see that it's not 13,000 years BCE or B.C.  
> as some have been quoting but (the authors actually said 12,900)  
> years B.P., = "before present", which means approx. 11,000 B.C.
>
> There is another very interesting article just published, about  
> apparent evidence for a tsumani, inferred to have been caused by an  
> impact, 2300 years ago (=300 B.C.) in the New York City - Long  
> Island area.  See geology.com, which linked to a story in National  
> Geographic News:
>
> http://news.nationalgeographic.com/news/2008/12/081231-new-york- 
> tsunami.html
>
> have fun,
> Pete
>
>
> -----Original Message-----
> From: DonH <donhalterman at verizon.net>
> To: erich kern <efkern at earthlink.net>; Rockhounds at drizzle.com: A  
> mailing list for rock and gem collectors  
> <rockhounds at lists.drizzle.com>
> Sent: Sat, 3 Jan 2009 5:56 pm
> Subject: Re: [Rockhounds] Diamond clues to beasts' demise
>
>
> erich kern wrote:
>
>> !3,000 yrs BCE
>> > >
> http://newsvote.bbc.co.uk/mpapps/pagetools/print/news.bbc.co.uk/1/ 
> hi/sci/tech/7808171.stm?ad=1
>
> OK, now we have some clarity on w
> hat's being said:
>
> "...lonsdalite, or hexagonal diamonds, associated with meteorite  
> explosions."
>
> So this is some bad terminology. Pretty sad.
>
> Don
>
> -- 
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___________________________________
R. Peter Richards
rpr at heidelberg.edu
Morphological crystallographer

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