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NWA 6693   contributed by Steve Brittenham, IMCA 2184   MetBul Link
 
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View all entries for   Meteorite (2)   Steve Brittenham (108)


Copyright (c) Steve Brittenham, unless otherwise noted.
asdf   Achondrite-ung

Steve writes:
Photos:
1 - Fragments
2 - Full Slice (normal reflected light)
3 - Crystals and Metal Inclusions (animated GIF)
4 - EDX of Chromium
5 - Bubble Trains
6 - Voids with Inclusions (80x)
7 - Sulfide Inclusions (400x)
8 - Geometric Inclusions (760x)
9 - Metal Inclusions (700x)
10 - Crust (160x)

Video - NWA 6693 Fragment X-Ray Video.mp4

Before I retired, the electronics company I worked for had a nicely equipped materials sciences lab where I could occasionally take a meteorite in after hours to analyze. I had just acquired two full slices, several thin sections, a research plug, and some fragments from the edge of an odd but beautiful green meteorite that at the time was pending classification. I was able to play with some of these pieces a bit before it was formally named NWA 6693.

NWA 6693 is an anomalous chondrite paired with NWA 6704 and NWA 6926 (NWA 6693 was found as a complete stone, NWA 6704 as a highly fragmented group of pieces that largely fit back into one mass with some voids, and NWA 6926 as a small stone thought likely to be another piece from NWA 6704). They have been called a number of unofficial names – “Super Green”, “Green Monster”, and “pyroxenite” to name a few – and possibly because their interiors resemble terrestrial “olivine bombs”, there was even an initial theory suggesting it might have been material ejected from Earth’s mantle after a cataclysmic collision by some large object (that theory, however, was only short-lived as subsequent research described a new planetary body as its likely origin1).

The first two photos show NWA 6693 to be highly crystalline and generally of a single lithology, an exception being the odd homogenous inclusion to the right of center at the bottom of the slice in photo 2. Photo 3 is an animated gif showing a microscopic view of two focus points in a region with multiple crystals and a pair of metal inclusions (the animation is purposely slow to allow better viewing of each frame).

Metal is distributed unevenly throughout the meteorite. Scattered nickel-iron inclusions – some as high as 80% nickel – are prevalent in most but not all of it, with some portions additionally containing chromium (refer to my EDX results in photo 4). Other portions have little or no metal present. The video shows a rotating x-ray of two small fragments from different parts of the meteorite (the biggest is just under 25 mm across). The larger piece exhibits scattered metal throughout (seen as dark spots) while the smaller shows virtually none.

I met Tom Phillips a few years after my initial SEM and x-ray observations (Tom was well known within the meteorite community for taking extraordinary thin section photographs). He was kind enough to help me take several dozen photographs of two of my thin sections to add to a few I had originally taken in the materials sciences lab. NWA 6693 exhibits interesting bubble trains, voids with inclusions, odd geometric features, and bubbly fusion crust. Photos 5 through 10 show examples of these features.

Reference:
1 cosmochemists.igpp.ucla.edu/2012-3.pdf


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Steve Brittenham
 11/25/2016 12:08:22 PM
Hi Dennis and Doug and John. Being retired, I have a fair amount of discretionary time for my hobbies. So I really enjoy putting together the descriptions, both because often times I remember things I've forgotten, and it often brings up questions that I get to research to learn new things (despite acquiring for over two decades, I'm still very much an amateur!). As I mentioned to Paul recently, my goal is to try to put up things that might be informative and, when possible, unique. I feel like I've accomplished something if I can get interesting exchanges and new information via the comments. I've even made a few new acquaintances as a result of MPOD! But most important, thanks to everyone that takes the time to look, and to folks like you guys that provide comments.
MexicoDoug
 11/25/2016 9:31:58 AM
I second that Denis :-) Thanks again Steve for the work you put in and shared. Anything along these lines is very educational and great to see on MPOD! IMO if you have the mass that was sectioned or microscopically imaged, macro pics like here make it more fun! But don't let that stop you if you don't have time to submit the 'full story' :-) next time!
Denis gourgues
 11/25/2016 4:36:57 AM
...whaou the compl*te story !!!..congratulations.... #9 very nice flacks of iron........
Steve Brittenham
 11/24/2016 4:30:16 PM
Hi John. Yeah, I agree with your comments about NWAs. Some are pretty cool! I have one chondrite that "bleeds" (which I assume is attracting moisture out of the air in just the two spots that exhibit this phenomenon), and one that grew small hollow spheres and tubules immediately after cutting that dissolved into the air in a few hours (kind of like Zag's halite crystals, only quicker). I have another chondrite that has pockets of flakey, pure white material in vugs (it's not cutting or polishing abrasive!) that also grew material around one of them. I don't know if pictures of those kinds of things are appropriate for MPOD, but if so and people are interested, I can post a few microscope pics of those sometime.
John Divelbiss
 11/24/2016 1:07:58 PM
awesome meteorite and presentation. NWA 6693 is such a special NWA, like so many other unique types and sub-types from Antarctica and other hot deserts. these special meteorites have changed and will further change our understanding of the variety of source materials and parent bodies we have to collect. As as an early promoter and buyer of NWA's, before there were numbers assigned to them from some areas, it really is gratifying to see how well this "desert meteorite collecting endeavor" has been for the last 20 years. It is amazing. In those early days many purists argued that NWA's were "junk and that we should not waste our money on them because without coordinates they were worthless". Same goes for the unclassified that I respect every bit as much as the classified. Enjoy our NWAs and other desert finds because this was and still is a special meteorite collecting time guys...it will be difficult to repeat it in future decades. Happy Turkey Day!!!
Steve Brittenham
 11/24/2016 11:59:11 AM
Hi Doug and Denis. Thanks for the nice comments! (And thanks to those commenting on my previous posts that I didn't get a chance to thank earlier.) Sorry about the typo - I spend hours preparing and re-reading (and even ask friends to proof for me), but the 'achondrite' typo got past me! And I believe Tom has a website where he sells lithographs of his personal thin section pics - he has some really nice ones - so if you're interested, you can probably Google it. Again thanks, and Happy Thanksgiving to those in the U.S.!
MexicoDoug
 11/24/2016 8:44:38 AM
This is an amazing compilation of imaging. The x-ray video is magical - I've always wished this tool were available to see meteorites but this is my first time! Wow on everything, great job Steve. The paper you referenced is top heavy in information but seems to argue convincingly on several points that this is not likely a diogenite derivative. Incredible images of the inclusions and just loved the last one of the sharply defined and contrasty metal inclusions. If not for the turkey in the oven I could easily spend another half hour admiring this superb MPOD submission. Thank you Steve (and contributions from Tom) - deserves some lithographs :-)! PS typo: "NWA 6693 is an anomalous chondrite paired with NWA 6704 and NWA 6926" ==> achondrite
Denis gourgues
 11/24/2016 8:14:58 AM
...whaou the compl*te story !!!..congratulations.... #9 very nice flacks of iron........
 

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