[Rockhounds] Another extinction impact-13 KYA

[Dora Smith]

OK, so lonsdaleite is hexagonal, and is similar to diamonds, but is not 
actually a diamond.

Wonder who invented that six sided diamond notion - the authors, who seem 
flaky enough, or the media?

Yours,
Dora Smith
Austin, TX
tiggernut24 at yahoo.com
----- Original Message ----- 
From: "R. Peter Richards" <rpr at heidelberg.edu>
To: "Rockhounds at drizzle.com: A mailing list for rock and gem collectors" 
<rockhounds at lists.drizzle.com>
Sent: Friday, January 02, 2009 5:03 PM
Subject: Re: [Rockhounds] Another extinction impact-13 KYA


>I think the reference is to a diamond-like mineral with a hexagonal  atomic 
>structure, not a hexagon-shaped diamond.  Normal diamond  crystallizes in 
>the isometric (cubic) symmetry system.  Look up  lonsdaleite in a mineral 
>reference book; it's the analog for diamond  in the hexagonal symmetry 
>system.
>
> Since graphite, diamond, and lonsdaleite are pure carbon, they can be 
> considered structures formed from spheres (atoms) of one size only. 
> There are two different ways to put together spheres as densely as 
> possible (i.e. with as little open space among the atoms as  possible); 
> these are referred to as "closest packing" structures.   Diamond structure 
> has one form - cubic closest packing - and  lonsdaleite has the other - 
> hexagonal closest packing.  Graphite has  a lot of open space - it is not 
> a close-packed structure.
>
> Dana's System Volume 8 mentions that lonsdaleite is often associated  with 
> diamonds and with meteorites or impact sites, and is generally 
> microscopic.
>
> I think this is what is being referred to as "hexagonal diamonds".
>
> Pete Richards
>
>
> On Jan 2, 2009, at 4:05 PM, donhalterman at verizon.net wrote:
>
>>
>>
>>
>>
>>
>> &gt; The abstract mentions two
>> &gt; kinds of diamond particles found, and I think the terminology  is a 
>> little
>> &gt; more technical than six-sided diamonds.
>>
>>
>> Hi,
>>
>> Unfortunately
>> I don't have time to read these linked articles, but I've seen some
>> posted references to "hexagonal diamonds," and I'm thinking the
>> following might help (or maybe not...)
>>
>> A hexagon is a
>> 2-dimensional figure, which is Greek for "six sides." On the other
>> hand, a six-faced, equilateral, 3-dimensional solid is--a cube! Take a
>> look at a cube and count the faces. The crystallographic name for a
>> cube is a hexahedron. There are cubic diamonds; in fact, former list
>> member John Betts sells cubic diamond crystals on his website. These
>> form on earth as well.
>>
>> I don't know if that helps with the discussion here, but at least  it 
>> should be a fun fact.
>>
>> Best,
>> Don
>>
>>
>>
>>
>>
>> --- StripMime Report -- processed MIME parts ---
>> text/html (html body -- converted)
>> ---
>> -- 
>> _______________________________________________
>> Rockhounds at drizzle Mailing List
>> Subscription Services:
>> http://lists.drizzle.com/mailman/listinfo/rockhounds
>> List Home Page, with a link to the List Usage Policy:
>> http://www.eclecticlapidary.com/Rockhounds/index.html
>
> ___________________________________
> R. Peter Richards
> rpr at heidelberg.edu
> Morphological crystallographer
>
>
>
>
>
> --- StripMime Report -- processed MIME parts ---
> multipart/alternative
>  text/plain (text body -- kept)
>  text/html
> ---
> -- 
> _______________________________________________
> Rockhounds at drizzle Mailing List
> Subscription Services:
> http://lists.drizzle.com/mailman/listinfo/rockhounds
> List Home Page, with a link to the List Usage Policy:
> http://www.eclecticlapidary.com/Rockhounds/index.html