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Glassthrower
Vendor - Galactic Stone & Ironworks
*****

Reged: 04/07/05

Loc: Oort Cloud 9
Re: Meteorites to Avoid new [Re: Kent10]
      #6051491 - 08/28/13 08:58 PM

The main source of contamination during prep work is chlorine from tap water. Many cutters use tap water to save time and money. One should only use distilled water to cut meteorites. Why so many people ignore that is beyond me, because distilled water is cheap.

The second main source of instability is insufficient drying after the prep work. Once a meteorite is cut and/or polished, it should be baked in a hot oven for several hours to purge remnant moisture.

Failure to observe those two simple rules results in many unstable pieces and disappointed collectors.

There is little way to tell if a specimen is unstable unless it is already showing signs of rusting. Over time, you will see which specimens are stable because the unstable ones will start to bloom little rust spots or weep a reddish-brown liquid.

Stones are much less problematic. Ideally, your irons and stony-irons should be handled only rarely and wiped clean with an oily cloth after handling. Store or display the specimen in a climate-controlled area in an airtight container that has dessicant inside it to absorb ambient moisture. This will retard any stability issues, but will not fix them.

Best regards,

MikeG


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Kent10
scholastic sledgehammer
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Reged: 05/08/12

Re: Meteorites to Avoid new [Re: Glassthrower]
      #6051538 - 08/28/13 09:37 PM

Thanks for the advice Mike. I did buy the Rocks from Space book so I will learn more soon. Is the "oily" cloth something special. I couldn't find many references to this specifically and none for sale. Thanks.

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Michael Rapp
Post Laureate
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Reged: 04/27/04

Loc: Dickinson, TX
Re: Meteorites to Avoid new [Re: Kent10]
      #6052891 - 08/29/13 04:12 PM

Mike, would it be a good idea to bake any meteorite one acquires in an oven as a precaution, or it is useless as any damage from remaining moisture would have already been done?

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Glassthrower
Vendor - Galactic Stone & Ironworks
*****

Reged: 04/07/05

Loc: Oort Cloud 9
Re: Meteorites to Avoid new [Re: Michael Rapp]
      #6053027 - 08/29/13 05:43 PM

Hi Michael,

Good question. In my experience, it's not really needed if the specimen appears stable and doesn't exhibit any outward signs of rust or lawrencite disease.

Stones are a special case. For the most part, they are very stable for collectors. They will rot if left exposed for prolonged periods in the field, exposed to the elements. But, in the average collector's air-conditioned environs, they hold up very well or indefinitely.

However, a few stones are known to be problematic. I didn't mention them earlier because the original post was about irons, but I should list them now. Also, the main culprit that afflicts stony meteorites is "lawrencite disease".

Ghubara - this one can be a prolific ruster and is prone to lawrencite. Why? Honestly, nobody has studied it and nobody can say for sure. I think it's a combination of long-term exposure to irregular rains on the semi-arid Omani plateau, and improper handling/storage/preparation in subsequent possession of hunters, middle men, and dealers.

Ghubara (and some others) may develop little reddish or brownish spots that look like common rust. In fact, it is a reddish fluid that is the result of a chemical chain reaction in the meteorite itself. It will soon weep more and more. You can wipe it down, clean it with a stiff brush, and bake it in an oven. And it will help the appearance, but the lawrencite disease is still lurking hidden in the matrix of the meteorite. It will continue to "bloom" these little beads of rusty liquid and the specimen will actually start to break down and become more friable. Slices may break or pieces will break off. Brecciated meteorites with this affliction can actually fall apart over time.

The cause of this is the introduction of molecular chlorine into the matrix of the meteorite. This is due to terrestrial contamination in the vast majority of cases. For example, using tap water as a coolant during cutting will introduce chlorine into the meteorite. No matter how well you dry the specimen afterwards, the chlorine will remain - it will react and bond with some of the material in the meteorite. These reactions produce a variety of effects, but the most noticeable is the weeping of reddish fluid.

This can be completely avoided by using distilled water during cutting and polishing. Baking them in the oven afterwards is a good "double-whammy" to prevent stability issues in prepared specimens.

Any dealers reading this who do not use distilled water and baking, please take notice now. The most important step in any prep is the saw coolant and distilled water is essential to avoid contamination of any kind. (lawrencite or otherwise)

Back to the point of the original post, no, you don't need to bake your meteorites. But, if they exhibit signs of problems, then you might want to consider it. If you stick to oven temps of about ~225F to ~240F, and don't bake for more than ~16-20 hours, then you cannot hurt a specimen by doing this.

Be careful baking etched irons - high temps and prolonged baking can damage the appearance of the Widmanstatten pattern and may require the meteorite to be re-etched.

Best regards,

MikeG

PS - that's the short answer.


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Glassthrower
Vendor - Galactic Stone & Ironworks
*****

Reged: 04/07/05

Loc: Oort Cloud 9
Re: Meteorites to Avoid new [Re: Glassthrower]
      #6053030 - 08/29/13 05:45 PM

Almost forgot, more stony meteorites known to have issues - Saratov and SAU 001. Some NWA desert meteorites also.

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Michael Rapp
Post Laureate
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Reged: 04/27/04

Loc: Dickinson, TX
Re: Meteorites to Avoid new [Re: Glassthrower]
      #6054457 - 08/30/13 01:23 PM

Thanks Mike, this is a fascinating hobby to be sure.

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lee14
super member


Reged: 12/19/09

Re: Meteorites to Avoid new [Re: Kent10]
      #6057459 - 09/01/13 11:20 AM

Kent, your pictures are excellent. Mike's information is certainly right on the money. I can't speak to the preparation and stability of chondrites, my experience with them is limited. I do however have a fair amount of experience with irons, having been collecting and sectioning them for 14 years. While it is certainly true that tap water should never come into contact with a specimen, most of the chlorine contamination that produces the ferrous compounds resulting in lawrencite comes from the environment, not necessarily from the cutting process. This is evident where complete specimens are involved, I've seen many a Campo that just ooze that greenish-yellow residue that results in the surface flaking away that have never been contaminated by municipal water. The chlorine was introduced by the terrestrial environment long before the specimens were collected. If one desires to keep such a specimen whole, the entire stone can be treated with appropriate means to remove the chlorine and 'stabilize' the specimen. As Mike stated, an etched specimen should never be treated this way, the etch will almost certainly be affected.

I cut all my irons with rain water, utilizing a cutting additive that does not contain chlorides. Once sectioned, the pieces are treated to a submersion bath that with remove any chlorine from the slices. After the treatment, the slices are rinsed long enough to remove any remaining solution that has penetrated into the surfaces, then dried for a couple of hours at 250 degrees. The surfaces are finished by sanding, and depending on the type of iron, polishing, without the introduction of any moisture. They are then etched with a solution of nitric acid in alcohol (nitol), rinsed thoroughly in alcohol and dried again. There's no point in using anhydrous alcohol for this, it's expensive and will absorb water from the atmosphere anyway. Gun oil (I like G-96 brand) is used to protect the surface from environmental moisture after finishing. Even properly prepared specimens can rust over time, and the oil will prevent this. There's no need to keep the slice heavily coated, just apply liberally and allow to penetrate the surfaces, then wipe off the excess. This application will also deter fingerprints from degrading the etch.

Lee


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Kent10
scholastic sledgehammer
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Reged: 05/08/12

Re: Meteorites to Avoid new [Re: lee14]
      #6058591 - 09/02/13 01:35 AM

Thanks Lee. I appreciate all the information. I have since collected another couple. The iron is my most expensive so far. I am going to have to slow down soon. But I wanted to get started with something and then start reading up and learning more.

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lee14
super member


Reged: 12/19/09

Re: Meteorites to Avoid new [Re: Kent10]
      #6059040 - 09/02/13 11:12 AM

I'd recommended 'Rocks From Space' and 'The Cambridge Encyclopedia of Meteorites', both by O. Richard Norton if you haven't already read them. Also 'The Robert Haag Collection of Meteorites' has an outstanding selection of photographs, and Bob himself is a great guy to know. Good luck!

Lee


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Kent10
scholastic sledgehammer
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Reged: 05/08/12

Re: Meteorites to Avoid new [Re: lee14]
      #6059058 - 09/02/13 11:27 AM

Thanks for the book recommendations. I ordered both by Norton so far and the Haag looks great. I may have to get that too Thanks again.

Edited by Kent10 (09/02/13 06:48 PM)


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Kent10
scholastic sledgehammer
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Reged: 05/08/12

Re: Meteorites to Avoid new [Re: Kent10]
      #6059816 - 09/02/13 06:49 PM Attachment (11 downloads)

The new iron

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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Meteorites to Avoid new [Re: Kent10]
      #6059820 - 09/02/13 06:50 PM Attachment (9 downloads)

And another

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Glassthrower
Vendor - Galactic Stone & Ironworks
*****

Reged: 04/07/05

Loc: Oort Cloud 9
Re: Meteorites to Avoid new [Re: Kent10]
      #6060265 - 09/02/13 11:37 PM

Taza and NWA 869?

Quick guess.


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Glassthrower
Vendor - Galactic Stone & Ironworks
*****

Reged: 04/07/05

Loc: Oort Cloud 9
Re: Meteorites to Avoid new [Re: Glassthrower]
      #6060275 - 09/02/13 11:40 PM

Agree with everything Lee said about preparing irons - he has much more experience with irons than I do. I have curated some in my personal collection, sold many of them, and sliced a small handful of them. But I have no experience with polishing, etching them. And my overall preparation experience with irons is minimal. Frankly, I just don't have the patience or skillset to excel at preparing irons - it's like astrophotography in that respect. It's the one of the hardest types meteorites to prepare, but the payoff is really high if you master it. If that makes any sense.

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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Meteorites to Avoid new [Re: Glassthrower]
      #6060280 - 09/02/13 11:46 PM

Quote:

Taza and NWA 869?

Quick guess.




You got it. Both of them. I really like those markings in the Taza and I like that these are whole slices.


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Kent10
scholastic sledgehammer
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Reged: 05/08/12

Re: Meteorites to Avoid new [Re: Kent10]
      #6060366 - 09/03/13 01:04 AM Attachment (7 downloads)

This one was inexpensive so I got it. It appears to have rust on it but I liked the way it looks. I bet you know this one too . . .

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Glassthrower
Vendor - Galactic Stone & Ironworks
*****

Reged: 04/07/05

Loc: Oort Cloud 9
Re: Meteorites to Avoid new [Re: Kent10]
      #6060380 - 09/03/13 01:24 AM

Nantan?

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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Meteorites to Avoid new [Re: Glassthrower]
      #6060406 - 09/03/13 02:00 AM

Yep. Nantan.

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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Meteorites to Avoid new [Re: Kent10]
      #6061460 - 09/03/13 06:30 PM Attachment (9 downloads)

I might as well add my latest acquisitions too. I really am almost done for awhile though

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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Meteorites to Avoid [Re: Kent10]
      #6061461 - 09/03/13 06:31 PM Attachment (9 downloads)

Another

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