Brad
starting to spend too much on rocks
Member since July 2006
Posts: 161
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Post by Brad on Oct 2, 2009 23:12:18 GMT -5
I have been asked to try polishing a batch of small meteorites in my rotary tumblers. Has anyone done this? Or, can anyone give me any tips on tumbling softer rocks?
I normally tumble various forms of quartz (agate, jasper, pet wood, etc.). The owner of the meteorites thinks they are about 4 on the Mohs scale.
Any suggestions? How much of the meteorites should I put in my 6-pound tumbler? What should I put in to cushion it? How much of what size grit? How long? etc., etc.
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darrad
fully equipped rock polisher
Member since September 2006
Posts: 1,636
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Post by darrad on Oct 3, 2009 7:59:41 GMT -5
I can't help with how to polish them but if they are indeed Meteorites I would try to talk the owner into keeping them as is. They are off world and made it all this way from who knows where so I personally would not change them.
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Post by Hard Rock Cafe on Oct 3, 2009 8:37:39 GMT -5
It is incredibly unlikely that they are meteorites. See: meteorites.wustl.edu/meteorwrongs/meteorwrongs.htmIf they have a fusion crust, that will be tumbled off, thus removing evidence that they are in fact meteorites. I don't believe they would polish in a tumbler, either. Sorry to be so negative. Have your friend have them positively identified as meteorites and then leave them alone. Chuck |
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Brad
starting to spend too much on rocks
Member since July 2006
Posts: 161
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Post by Brad on Oct 3, 2009 9:21:00 GMT -5
The owner of the meteorites is a well-respected geology professor. His main expertise is fossils (he's written several excellent books), but I'm sure he knows how to identify meteorites accurately.
The owner has a lot of them & wants to try polishing some. I'm honored that he asked me to help.
They might not polish in a tumbler. I'm not sure that anything that soft would. But we are going to try, so I'd appreciate any tips that will give us the best chance of success.
Hard Rock Cafe, it is an interesting coincidence that you pointed me to a page on the Wash. U. site. I was showing off some slabs I had tumbled at our rock club meeting last night. The owner of the meteorites (whom I've know for 2-3 years) saw them, admired their polish, and asked if I would try polishing some of his meteorites. Our rock club meets in the Earth and Planetary Sciences Building at Wash. U.! (BTW, the meteorite owner teaches at a different college in our area, not at Wash. U.)
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carloscinco
fully equipped rock polisher
Member since July 2008
Posts: 1,639
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Post by carloscinco on Oct 3, 2009 15:24:19 GMT -5
I have several egg sized meteorites that have had one end polished. The rest of the meteorites retain the fusion crust. The polished faces show the granular makeup of the stone as well as the iron/nickle inclusions. The faces on these meteorites were polished on a wheel. I think you would lose most of the stone if you tumbled due to the thermal and impact stresses the stone went through. Without the fusion crust it will look like any other rock.
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Post by Hard Rock Cafe on Oct 3, 2009 22:15:30 GMT -5
Well Brad, I stand corrected. I guess a geology professor should know. I've just encountered several people with rocks that don't look like anything they've seen before and they've jumped to the conclusion that they must be meteorites.
I think Carlos is on the right track.
Chuck
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Post by connrock on Oct 4, 2009 5:53:50 GMT -5
I don't know if this will help but it's a good recipe for soft materials,,,,
How to tumble Petosky Stones
Step 1: Start with 320 or 500 & finer silicon carbide grit, using a
thickening or suspending agent like syrup, sugar, or molasses for
cushioning.
Step 2: Use 600 or 800 & finer silicon carbide grit with a ratio of 1 to 1 or
2 to 1 of media to Petoskey stones. Use plastic pellets or coarse-ground
walnut shell for media. You may also need to use a thickening agent like
syrup, molasses, or sugar (being careful not to thicken load excessively).
If you use 600 silicon carbide grit, follow with 600 aluminum oxide as a
pre-polish, jumping to the final polishing stage.
Final Step: Use cerium oxide or 0.5 to 0.8 micron aluminum oxide polish,
cushioning with fine-ground walnut shell and a thickening agent like
syrup, molasses, or sugar, but do not thicken load excessively.
connrock
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Brad
starting to spend too much on rocks
Member since July 2006
Posts: 161
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Post by Brad on Oct 4, 2009 22:15:13 GMT -5
Thanks Connrock! Do you know how long each of those stages lasts?
How much rock (meteorite) can I put in a 6# tumbler? I'm guessing 2/3 full in step 1. In step 2, 2/3 full of rock + media? Same in final step?
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SirRoxalot
freely admits to licking rocks
Member since October 2003
Posts: 790
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Post by SirRoxalot on Oct 5, 2009 23:15:15 GMT -5
Are they nickel-iron meteorites, or stony? The former could be gently tumbled to remove oxidation and shine the exteriors, the latter.... I dunno. Tumbling them is quite... unusual to say the least.
Are you aware of how valuable meteorites are? Are they from a known find? Identified by a meteorite expert?
I'd STRONGLY suggest you slab them, which is normal practice for meteorites. True meteorites are too rare and cool to be chucked into a tumbler as an experiment. If you want to shine them up, for some reason, use a diamond grinder, same as you'd cut a cab. Run thru the wheels and then polish, if nothing much happens then you have your answer.
-edited for spelling lol-
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Post by connrock on Oct 6, 2009 4:35:44 GMT -5
I really hate to help you tumble these but you asked so I will help.
I would use a lot of soft media throughout the entire process.
about 1/4 meteorites.3/4 pellets.
it may take longer but it will insure that you don't ruin them.
connrock
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MikeS
fully equipped rock polisher
Member since January 2009
Posts: 1,081
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Post by MikeS on Oct 6, 2009 17:26:23 GMT -5
I agree, I wouldn't polish them. I'm guessing that if you are asking how to polish them then they are too small to slab. If they are big enough to slab, I'd say do that instead of tumbling them. As noted above, polishing them will pretty much ruin their value as specimens. Meteorites are cool, I have a small metal one in my collection, I found it on the badlands west of where I live, and positively ID'd by the local geological museum...very cool just the way it is!   |
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