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Best Etched Meteorites?

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#51 lee14

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Posted 15 September 2013 - 10:27 PM

I believe def clear coat is simply automotive lacquer without pigment.

Lee

#52 Kent10

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Posted 15 September 2013 - 10:28 PM

Yes an advantage of these coatings is that it will protect nicely but if it compromises the look... In my 1st Taza I can actually see scratch marks made in the coating and it is so reflective. I don't mind the Gibeon one. It still looks quite nice but I would sure like to see it without the coating. I also like the gun oil method :) Perhaps when my irons start rusting or looking not so good I will have wished I had them all coated :)

#53 lee14

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Posted 16 September 2013 - 08:22 AM

That Taza certainly has a lot going on. The inclusion is either troilite or graphite, can't be sure from a pic. The underlying Widmanstatten pattern is quite muted, but attractive. Those needle-like forms are really spectacular, and probably schreibersite, Mike would probably have a better estimation. Then there are a couple of more amorphous metallic formations at 5 o'clock from the troilite. These look just like those one often sees in Canyon Diablos. I'd say this material underwent some serious shocking.

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#54 Kent10

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Posted 16 September 2013 - 08:25 AM

I like it and I hope it looks as good in person. Here is the reverse side and a close up of the inclusion.

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#55 Kent10

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Posted 16 September 2013 - 08:26 AM

Close up

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#56 Kent10

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Posted 16 September 2013 - 08:27 AM

Other side close up

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#57 lee14

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Posted 16 September 2013 - 12:00 PM

I'm going to say troilite rather than graphite. It has the brownish tinge characteristic of troilite (iron sulfide) rather than the grayer look of graphite. What I especially like about this one is the metal crystals arranged around the perimeter. Really nice!

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#58 Glassthrower

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Posted 16 September 2013 - 04:13 PM

That is an awesome Taza. The inclusion is surely graphite, but it appears to have a ring of schriebersite around it. I'm not familiar with the chemical makeup of Taza in particular, but when one sees graphite inclusions like this in an iron meteorite, there is often a ring of schriebersite around them.

Let me preface my next statement - I am not skilled with iron meteorites and I am not particularly knowledgeable about them because I don't collect them and rarely sell them. It's not a knock on irons, it's a restraint I put on myself because the high expense and learning curve of prepping and curating irons.

Also, I live in Florida, which presents a constant battle with humidity to keep my specimens from degrading while in my possession. Plus, as Lee will attest to, irons are rough on the saw, blades, and equipment. But, I have picked up some knowledge of curating iron meteorites from Pat Mulvany. Some of his knowledge rubbed off on me via osmosis over the years. I do know that coatings are generally harmful to most meteorites - in terms of contamination and loss of scientific study value. However, many irons desperately need to be saved from oxidation, so using chemical or oil treatments and coatings is a necessary evil with irons. The only big exception to this is uncut irons that have a stable, protective shale rind around the unoxidized core. Those can last almost indefinitely in a stable state if they are properly stored and handled.

Best regards,

MikeG

#59 lee14

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Posted 16 September 2013 - 05:26 PM

Is it the ring of schriebersite that leads you to the conclusion that the inclusion is graphite? I've never worked with a Taza, but the only place I've seen graphite inclusions are Canyon Diablos. The only non-intrusive test I know to differentiate between the two is that troilite tends to stain the surface if one is slow to halt the etching process. If you've got a visual method of telling whether an inclusion is graphite or troilite, please fill me in!

Lee

#60 Glassthrower

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Posted 18 September 2013 - 05:51 PM

Is it the ring of schriebersite that leads you to the conclusion that the inclusion is graphite? I've never worked with a Taza, but the only place I've seen graphite inclusions are Canyon Diablos. The only non-intrusive test I know to differentiate between the two is that troilite tends to stain the surface if one is slow to halt the etching process. If you've got a visual method of telling whether an inclusion is graphite or troilite, please fill me in!


No, the ring of schriebersite is just coincidental - you see similar rings around various inclusions, clasts, or even around armored chondrules in some stony types.

I am guessing this is schriebersite, but I am not sure. The schriebersite would be the innermost ring around the inclusion, and the lamellae radiating outward from it are probably the usual taenite or kamacite.

As for the inclusion, graphite is my guess, but I am not 100% certain - I probably sounded more certain at first, but after studying the photos more closely in Photoshop, I am not sure now - it could be graphite or troilite. I am still leaning towards graphite because of the color and apparent texture in the photo. The majority of easily-identifiable troilite I have seen has a brassy hue to it. But, troilite doesn't have to be brassy - it can appear greyish or it can have the same hue/color as the other metal in a given meteorite.

In general, most graphite inclusions are a bit darker in appearance than this one. And, as far as I know, graphite is not common in Taza (NWA 859). So I could be very wrong on this. A hardness test on the inclusion might narrow down the possibilities - graphite is softer than troilite, unless it is so highly shocked that the graphite has become hardened.

I would try scratching the surface of the inclusion and find out what the hardness is. Graphite is 1.5 on the MOHS scale, so you should be able to scratch it with your fingernail. If you can't scratch it easily, then it's likely not graphite - unless it is highly shocked.

Best regards,

MikeG

#61 lee14

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Posted 19 September 2013 - 08:07 AM

It occurred to me a streak test might be informative, but they seem to be fairly close in appearance, graphite leaving a black, and troilite grayish-black. Streak combined with hardness tests should give a pretty good level of certainty, but I think qualitative analysis would be the only completely accurate determination. Thanks Mike!

Lee

#62 lee14

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Posted 19 September 2013 - 12:26 PM

This is definitely a graphite inclusion, in a Canyon Diablo. The overall pic is poor, but I tried to make the appearance of the inclusion as faithful as possible to the actual color seen in daylight. It's gray, not a hint of brown. For what it's worth...

Lee

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#63 Kent10

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Posted 26 September 2013 - 03:59 PM

I received the Taza today. It is just unbelievably beautiful. And there is no contest when compared to my 1st one with the coating on it. The new one sparkles. So glad I got it!

I wish it was easier to tell from pictures what these irons will look like when you get them. Some are bright and when changing angles in the light different spots light up. But then I have others that are dull looking and in light it is difficult to get the same effect. Best to buy in person I suppose if at all possible.






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