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Franconia Iron with chondrites?


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Several Franconia chondrites have been found in recent years that appear to have irons embedded within them. The theory is that these irons separated from the main chondritic mass during atmospheric entry. This makes sense, the density of the iron masses being nearly twice that of the chondritic mass would cause them to punch their way out as the G forces reached a maximum level.

Many Franconia irons have small craters scarring their surface, often with a lop of lipping around the outer edge. Most people believe these craters are the result of chondrules that were embedded or adjacent to the irons. Could be....maybe, but I dunno....

I have collected over 100 of these small irons so far. Most of them are covered in rust or caliche. After removing the caliche with CLR most of these irons seem to have melted metal surfaces, often exhibiting lips, nose cones, flow lines, etc. A very few appear to have a bubbly fusion crust. The pics below are from one of the irons I found a few days ago at Franconia showing a 0.3 gram iron with a bubbly fusion crust. Several of the bubbles have ruptured leaving a hollow crust, almost like an eggshell. My first thought when looking at this with a 10X loop was that these must be chondrules that burned up during entry. But they are too small, smaller than most chondrules (the pics were taken on a 1cm cube to give some size comparison). To prove that this is an iron and not a chondrite I polished one end to expose the metal as can se seen in the 2nd pic. Also, while polishing it I noticed that the fusion crust appeared to be glassy or similar to fusion crust on a chondrite. The ruptured bubbles can be explained in several ways: 1) they could have been chondrules which heated during the entry phase and gasified bursting through the liquid crust. 2) the liquid fusion crust of the chondrite could have encapsulated the tiny iron and perhaps it was sort of boiling from atmospheric entry when it suddenly cooled and froze the bubbling surface 3) The bubbles could be ordinary chondrites attached to the exterior of the iron and have simply weathered away exposing empty shells of the chondrites.

Anyway, just thought I would share these pics and see what others might think. Has anyone else observed this? Please share your thoughts....thanks.....jim

Oh, the last pic shows the Franconia iron next to a similar size Franconia chondrite for comparison. Note the smooth fusion crust of the chondrite. I believe there must be tens of thousands of these small Franconia chondrites out there still because I continue to find them stuck to my magnate yet they are too small to sound off my detector....but that is another story!

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Edited by Paleomanjim
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Jim,

You should talk to Troy Ball, I think his last count was 800 or something like that, and I believe he has a few like that.

Dave.

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Jim,

Nice pictures and good info to consider about the special little irons.

I had to replace that tire when I got home but maybe I could have put tire seal in it?

Hope to see you again.

Mitchel

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All of the irons in the Yucca Dense Collection Area (Franconia) that I had tested are H-Metal. So it's not uncommon

to find chondritic material attached to them.

Jim

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Mitchel, I soak my irons overnight in pure CLR. Some collectors consider this too harsh, but it works well for me and I have had no damage to any of the metal features. When doing this the irons with a heavy caliche will bubble for an hour or more. After 12 hours or so most all of the caliche will be disolved away, although some rust may persist on heavily rusted specimens. The rust can be removed with more soaking a scrubbing with a toothbrush but I usually avoid scrubbing them and live with a bit of rust. After removing them from the CLR I wash them with water, dry them and then soak them overnight in olive oil (because its what I had). Dry them well again. They take on a dark look, sometimes bluish on leading metal edges, and fine lips and flow lines can be observed. I keep them in sealed plastic bags and some that I have had for 3 years look the same as when I stored them.....

Jim, Of the 100 or so that I have only 3 show anything like this, so for me at least it seems a bit rare. And of the 3 this one is the strangest. The bubbles are not attached chondrules in my opinion for 2 reasons: First, they seem a bit too small. Second, why would the interiors blow out when attached to an iron when they don't blow out on chondrites? So it begs the question: What caused the bubbles? Are they the result of atmospheric heating or boiling of some type? The fact that several appear to have burst or blown their tops off leaving hollow shells is a clue in my opinion.....jim

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My guess is that you found a well preserved cornflake variant.

You have lost me about the blow out thing. Who says anything blows out??? I am not most people, by the way.

The bubbles can occur by outgassing when the thing was passing though our atmosphere and mixing with our air. Think about it...what happen when you heat a sulfide? Ever cut a chondrite using water and smell the sulfides? Fairly typical.

Metal is a great conductor of heat and expands when heated at a different rate than that of the matrix that held it together in space. This may possibly be one answer why we see these separated from their parent body. We do have evidence of these cornflakes being metal veins in H chondrites from the Yucca DCA. Pictures of them sticking out of a good sized stone, etc.
If you take a Yucca meteorite with a known vein in it an apply pressure to it, it will break apart at the weak link. And that weak link will likely be the boundary between the metal in the vein and the matrix.

Also note that there is no observation of these "craters" beyond the heat affected zone that could be inspected to date. Recently another iron appeared from another fall....which I believe Michael Farmer holds. Nice and new and fresh. It too has "craters" which are nothing more than outgassing.

You could probably take a pin punch and wack one of those bubble looking things and it would break open or not! Regardless, I don't think there is much mystery to it. The real mystery is which chondrite did your h-metal come from???

Jim

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Jim, who said you were "most people"? What do you mean by that? I'm just sharing some pics of an unusual iron, or at least I thought it was unusual. And sharing my speculation on what I think caused it. I have never read any literature on meteorites describing anything like this. The description of "blow out" is my own, I thought it was obvious. Apparently there is no mystery at all....

Edited by Paleomanjim
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Jim,

"Most people believe these craters are the result of chondrules that were embedded or adjacent to the irons."

I meant I do not agree with most people in that train of thought.

In regards to whether it's an iron or a chondrite. If the vast majority of the specimen is metal, then it would be an

iron. There are meteorites found there that have a bunch of iron in them....but because there is so much chondritic matrial, they are considered chondrites.

Nice find, Jim. Congrats!

Jim

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