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Opinions, please, on what this is

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#1 molniyabeer

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Posted 04 May 2008 - 05:49 PM

A few weeks back I bought a large lot of unclassified NWA stones to resell at a fund raiser. Mixed in with the batch was this fellow. Most of the stones were quite fine grained and showed few if any obvious chondrules, and even those were pretty tiny.

Then there is this. It is a rounded grain about 5mm across and appears to be firmly embedded into the matrix. The grain is zoned concentrically. The rest of the matrix appears to lack chondrules that I can see with the hand lens. The sample is magnetic as shown in pic #4.

Any ideas? Feel free to re-send the pics to anyone you think might have some insight.

Thanks and Clear Skies.

Attached Thumbnails

  • 2371318-Web NWAXXX_Chondrule1.jpg


#2 molniyabeer

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Posted 04 May 2008 - 05:49 PM

#2

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  • 2371319-Web NWAXXX_Chondrule2.jpg


#3 molniyabeer

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Posted 04 May 2008 - 05:49 PM

#3

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  • 2371321-Web NWAXXX_Chondrule3.jpg


#4 molniyabeer

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Posted 04 May 2008 - 05:50 PM

#4

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  • 2371322-Web NWAXXX_Chondrule4.jpg


#5 Glassthrower

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Posted 04 May 2008 - 07:02 PM

Steve,

Here are some possibilities :

1) it's a large chondrule. Chondrules can be quite big, and they can seperate from the parent mass. What you have may be a large chondrule that was in the process of ablating out, but the ablation never completed. Had this chondrule been removed (or burned away), it would have left a regmaglypt or similar void, or possibly caused the piece to fragment further.

2) it's an anomalous inclusion. It could be a "CAI", which is a "calcium, aluminum" inclusion. This is very old matter, older than the surrounding matix material and possibly was left over from the solar nebula. Or it could be some other mineral inclusion (a big fluke rogue chondrule essentially).

3) It's something terrestrial that become lodged/fused to the meteorite on impact or during weathering.

I've seen a couple of UNWA's with big chondrules and inclusions, but nothing that looks exactly like this one you have. It's neat, whatever it is. It gives the stone character. Only a lab classification will reveal it's true nature.

Regards and clear skies,

MikeG

#6 abbsconey

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Posted 04 May 2008 - 08:09 PM

My 1st impression is a fossilized snail, but hey what do i know. :grin:

Wonder how it looks magnified.
It looks pretty cool, definately a "keeper".

#7 molniyabeer

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Posted 04 May 2008 - 11:33 PM

Mike/Todd, thanks for the ideas.

Mike, the surface it's on strikes me as more weathered than fresh, so don't know how much material might have weathered off to leave it in such high relief. It appears like it fractured across the grain and then weathered a bit more (the rough surface of the grain is slightly smoothed), so maybe the parent stone fractured, perhaps plucking part of this out of the other half of the stone?

The concentric layering inside it is odd. The larger chondrules I've seen in thin section photos have all been either agregates or more fan-shaped crytal forms without such a distince rind or rim.

As you say, an interesting piece to be sure.

Clear skies.

#8 csa/montana

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Posted 05 May 2008 - 07:42 AM

Thanks for the photos; indeed that is a most interesting item!

Carol


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