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Rust with Nantan meteorites

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#1 LivingNDixie

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Posted 27 May 2008 - 07:02 PM

Are these bad for rust as a whole?

#2 Glassthrower

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Posted 27 May 2008 - 07:20 PM

Nantan has a reputation as a "ruster".....but there are exceptions.

Nantan was a large fall with a strewnfield that covers a wide area - some of the Nantan meteorites were found below the water table. They were in moist ground in areas of high humidity, and thus they have a predisposition to rust. Most are rusted when they are found - the rust is mechanically or chemically removed (or both) and a "clean" Nantan is sold. The problem is, moisture has intruded into the matrix of the iron - meteoritic iron is a complex alloy that was formed by slow crystallization. It's also heterogenous. So, water has inroads into the interior of the iron. Over time, the oxidation will resume or worse yet, "lawrencite disease" may set in, which is a different affliction.

Some Campo Del Cielo meteorites also have this reputation - Argentina is a diverse landscape, and the Campo strewnfield covers areas that are densely forested and cut through with rivers. Campos found down low in the valleys are rusters - Campos found on the slopes, above the treelines, are not rusters. There is no real way to determine which is which if the specimen has been cleaned off. Over time, you will notice that some irons and stony-irons will oxidize faster than others. My Campos are slowing starting to show oxidation, as are my Nantans and Odessas. My Sikhotes are still rust free, but Sikhote is famous for being resistant to rust and lawrencite disease.

My advice is, go ahead and buy Nantan, just be careful who you get it from. Nantan and some indochinites sold on eBay are not what they claim. There is also bogus moldavite going around on eBay. Get your Nantan from a reputable dealer (IMCA or Meteoritical Society credentials, or both) and make sure you buy a specimen that is rust-free (or darn close to it) when you first get it. Then, once you get it, clean off any remaining rust with a stiff wire brush. If you have to rinse away debris, use WD-40 or a similar petroleum distillate that inhibits water. Treating an iron with petroleum distillates (or "Sheath" preservative) will forever leave it's mark - an oily feel and smell. But, rust will be largely prevented. Just wipe the specimen down after handling to remove skin oils, and then place it in a sealed air-tight container with a packet of dessicant to absorb trapped moisture. You will have no problems then.

Most oxidation issues arise from "display" and not "storage".

Regards,

MikeG

#3 LivingNDixie

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Posted 28 May 2008 - 05:30 PM

Thanks Mike!


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