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NWA xxx   contributed by Steve Brittenham, IMCA 2184   MetBul Link


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View all entries for   Meteorite (76)   Steve Brittenham (108)


Copyright (c) Steve Brittenham.
103.2 grams.   Unclassified

Steve writes:
We affectionately named the uncut 103.2 gram NWA in Photo 1 "the bleeder" because in the humid environment of Lake Oswego, Oregon, water would consistently wick up and pool at spots on the meteorite’s fusion crust (the process would take several days after wiping any prior accumulated moisture off, but it proved to be very repeatable). Consequently I purchased it several years ago with the admittedly naïve hopes that something really unusual was going on inside. But when I got it home to the drier confines of Boise, Idaho, the pooling immediately stopped (Photo 2 shows a microscopic view of one of the now dry "bleed sites").

When I finally did cut it there was nothing on the inside that gave any clue as to the reason for the moisture wicking, but it was still mildly interesting (Photo 3 shows the location of the cut and its size relative to a 1 cm cube; Photo 4 also provides a better view of its fusion crust along with some oxidized areas, some of which were "bleed sites"). An obvious breccia, under normal lighting the various lithologies are generally quite dark, as seen on the polished side in Photo 5; but the unpolished side in Photo 6 reflects light less and better stands up to intense illumination, making it easier to photograph some of its more subtle characteristics. Photo 7 shows a pair of shots at different lighting that accentuates the melt characteristics on the polished half.

Despite not wicking up moisture in Boise’s drier environment, the interior of the meteorite has proven to be quite prone to oxidation, with the unpolished side more so than the polished one (to the contrary, I would have thought that moisture from polishing would have made oxidation issues worse); as seen in Photo 8, the unpolished cut developed several large oxidation sites over the five years since it was halved, while basically only the metal in the unusual inclusion on the right of the cut face in Photo 5 rusted out (Photo 9 shows the cavity left by the now oxidized metal).


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Steve Brittenham
 5/5/2017 5:18:26 PM
Hi John. Thanks for the explanation. And no worries about the alcohol and/or acetone bath/soak part . . . I'm guessing everyone routinely does that anyway after cutting or prepping meteorites, so it probably goes without saying!
John Divelbiss
 5/5/2017 4:48:06 PM
The process is likely oxyhydration of lawerncite in the "rock" when in contact with water or moist air. It happens when the right mix chlorine, iron, nickel mixes in space rocks occur, both source and impactors. I think the baths, both glycol and brake oil, help to accelerate the oxyhydration process ending with it being stabiilized. And yes I use the alcohol bath/soak after cleaning the glycol off and before baking. I left that out.
Steve Brittenham
 5/5/2017 2:31:38 PM
Hi John. Thanks for the advice. While it hasn't "bled" since coming to Boise, the oxidation on the unpolished cut continues (though, surprisingly, not on any of the fusion crust). I might try your suggestion on that half as a test (I have used long automatic transmission fluid soaks on irons followed by acetone and alcohol cleaning then baking, as well as hot washing soda baths on irons wrapped in aluminum foil followed by cleaning and baking, both of which seem to work well; but I haven't tried treating any stones). And do you know the mechanism of the water wicking? Again, thanks!
John Divelbiss
 5/5/2017 1:03:05 PM
If you choose to do it, the meteorite volatiles/water/air chemical reactions like bleeding/oxidation can be eliminated (for the most part) with a nice 3 or 4 day soak in automotive antifreeze and then pulled out, wiped off, and then cooked at 400 F in the oven for a several hours to boil off all the glycol, water and volatiles. The hot temperature is for the glycol. I have "fixed" some bleeders like SAU-001 and Ghubara from this annoying problem. Also irons like Campo and Chinga have been helped by this method too, with longer soak and boil off times.
Steve Brittenham
 5/5/2017 12:30:21 PM
Thanks Wilford and Jansen. And Jansen (again, sorry for calling you Jason in my prior submission's reply), I'm not sure about the pooling, and I must admit I was disappointed not to see anything inside to explain its source. But as you can see from several photos (number 4 in particular), it probably had many sites at one time that "bled". One of the two sites that were present when I originally bought the meteorite is seen at the upper right of the rightmost shot in Photo 1. It would be great to hear of theories from anyone regarding what might have been going on!
Wilford Krantz
 5/5/2017 10:45:19 AM
Nice specimen!
Jansen Lyons
 5/5/2017 9:49:53 AM
Incredible NWA XXX Steve! Interesting about the pooling. Very unique back-story for the piece. Great interior breccia, too. All around amazing NWA. Thanks for the share! God bless!
 

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