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Meteorite inspection - Conception Junction issue

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#1 rfinney

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Posted 28 January 2013 - 11:22 PM

This week I finished my annual detailed one-by-one inspection of the specimens in my collection (about 2,800 total specimens). In the summer time I do a similar inspection, but not as detailed.

When I checked Conception Junction, which is in a sealed box with silica beads as a desiccant, I noticed some rust forming on the edges. I opened the box and found the specimen to be in pretty bad shape.

I am doing the usual recovery steps to salvage what remains, but I wanted to warn others to check their own Conception Junction specimens since this rusting really caught me by surprise, the slice had been looking stable during the last few visual inspections.

Other iron/pallasite specimens which required maintenance this time were:

Brenham (several specimens are slowly turning to dust)
Carlton (minor rust)
Campo del Cielo (some bright slices showed rust)
Goose Lake (minor rust)
Muonionalusta (some rust, no surprise, needs curation)
Nantan (some rust, no surprise here either)
Pedernales (minor rust)
Morasko (minor rust)

I also had two stone meteorites which required maintenance:

Travis County (a): Monnig specimen, I was surprised that it needed curation
Ghubara: one large cut specimen was lightly rusting - is that normal? - my others are fine

That was all that required attention during this specimen review.

If you have any of these you might check your own collections as well...

(Cross posted to the IMCA list)

- RF

#2 peter scherff

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Posted 29 January 2013 - 01:45 AM

Hi Russ,

Thanks for the heads up, I just checked my sample of Conception Junction and it is still pristine.
I remember when Ghubara was the cheapest stone that I could purchase. It was so inexpensive because it had a tendency to rust.

Peter

#3 Glassthrower

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Posted 29 January 2013 - 02:35 PM

Hi Russ, Peter and Curious Onlookers,

One of my main interests in meteorites since the beginning has been curation and preservation. While I lack a museum-class collection to curate, I have handled and dealt with a vast number of specimens over the years. I have had falls, finds, oddball types, whole stones, slices, irons, stony-irons, micros, etc, etc. I've also encountered or owned specimens with stability issues - rust, lawrencite disease, etc.

I have researched the issue of oxidation in meteorites of all types and I have discussed it at length with Pat Mulvany (who is an expert in curation and preservation). After much consideration, I have arrived at a conclusion regarding the stability of specimens on the collector market.

What is that conclusion? Well, it's not going to sit well with some, but I believe it is a fact of the market and it's not going to change unless it is brought out into the open. Premature oxidation is a preventable issue and it needs to be seriously discussed by those dealers and wholesalers who cut and prepare specimens for the market.

Here is the truth about meteorite specimen oxidation -

1) Every meteorite will experience some measure of oxidation, regardless of how well curated and preserved it is. Earth is toxic to meteorites. The best we can do is minimize and slow down this process to an acceptable level.

2) the vast majority of dealers are using preparation methods that lead to unnecessary instability and oxidation. These flawed methods are easily fixed and there is one major culprit that stands out above the rest - the introduction of water and chemicals into the specimen during preparation.

3) I am becoming increasingly convinced that some of the instability issues we see are due to the POLISHING PROCESS.

Ideally, a meteorite should be handled in a sterile environment and any terrestrial contamination (biological or otherwise) should be eliminated. This is almost impossible to do, unless you have a clean-facility like NASA's JSC meteorite repository. The most fundamental error that many dealers, curators, and cutters make is using tap water or chlorinated water during the cutting process. This has been discussed previously and is generally accepted as bad practice. It is become less common because it has been exposed as an easily-preventable issue. In the case of chlorinated water, it's just a matter of switching to distilled water. Problem solved.

But, meteorite preparation rarely stops at the first cut.

The freshly-cut specimens should be immediately put into a pre-heated oven (~225F) for at least 4-6 hours, and preferably upwards to 12-16 hours for problematic specimens (stony irons, silicated irons, or stones known for issues like Ghubara and Tsarev).

Like using tapwater during cutting, skipping the oven-baking step is a critical and easily-preventable error. 30 minutes to 2 hours is not enough time. It should be 4-6 hours at a bare minimum.

After this step in the process, the next step is typically sanding and polishing. There are several ways to go about this and numerous techniques and methods could be debated for different types of specimens. But generally speaking, there are dry-sanding methods and wet-sanding methods. The same can be said for polishing.

Typically, a powered "flat lap" or lapidary-wheel is used. This involves interchangeable grit wheels and the use of various diamond slurries and polishing compounds.

And this is the where, IMO and experience, the problem rests - the polishing process. Those slurries and polishing compounds contain a variety of chemicals and water or oil as a base. These polishing products are not specifically made for meteorites - they are made for polishing gemstones and rocks/minerals like agate. Therefore, it is likely that the water used in the manufacturing of these products is common tapwater from the local municipal supply. Or, perhaps one of the polishing compounds or slurries contains a problematic chemical that does not play well with meteorites.

I strongly suspect this is the case because I have seen numerous examples of this problem from some of the best dealers on the planet and from some of the best cutters in the business. These people have the proper equipment, skillset, and the resources to avoid these stability problems. But, I think they often overlook the contamination aspects of their preparation processes. I don't think it's cutting corners to save time or money, it just a matter of not being fully aware of the issue. Often, these specimens are prepared and sold in short order, and before the oxidation issue becomes apparent, the specimen is sold and the dealer is never subsequently informed of later stability issues. It's out of sight and out of mind, so to speak.

Collectors and dealers are often afraid to broach this issue or discuss it, for fear of offending someone or appearing to be pretentious. But the silence is allowing these practices to continue, to the detriment of the meteorites and collectors (institutional or private).

Back to the polishing and sanding - if wet sanding is used, or agents such as water/slurries/compounds are used during polishing, then these agents should be carefully screened for contamination potential. Furthermore, immediately after wet polishing, the specimens should go right back into a hot oven for another long baking session.

Any misstep, no matter how small it may seem, during this process will result in rusty or sick specimens.

Proper preparation, curation, and conservation will prevent most of these problems.

Best regards,

MikeG

#4 rfinney

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Posted 29 January 2013 - 09:31 PM


Mike:

Awesome discussion and feedback - great insights!

Best Regards,

- RF

#5 peter scherff

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Posted 30 January 2013 - 03:58 PM

Hi Mike,

I agree that we create many problems when we prepare the meteorites in our collections. I try to know everything that was done to the samples in my collection. But in the end it comes down to trust.

Most if not all of the "problem" meteorites are problems before they enter our collections. I have seen 2 kilo individuals of Ghubara ooze rusty liquid. I would love to know the history behind this meteorite. With problem meteorites we must take extra care to preserve them. Often no matter what is done they will still deteriorate.

Peter






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