Best Etched Meteorites?
Posted 15 September 2013 - 10:27 PM
Posted 15 September 2013 - 10:28 PM
Posted 16 September 2013 - 08:22 AM
Posted 16 September 2013 - 08:25 AM
Posted 16 September 2013 - 12:00 PM
Posted 16 September 2013 - 04:13 PM
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.
Posted 16 September 2013 - 05:26 PM
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.
Posted 19 September 2013 - 08:07 AM
Posted 19 September 2013 - 12:26 PM
Posted 26 September 2013 - 03:59 PM
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.