Mike I am new at rock tumbling also. I have Petoskey stones also. I read that since they are a soft stone you have to be real careful. The book told how to polish by hand. I tumbled mine for about 24 hrs. I used a medium grit. By looking at them, I am afraid to put them back in the tumbler with the polish compound. My plan is just spray them with lacquer. I haven't done it yet. Hope this helps. I am sure someone who has more knowledge and maybe has tumbled Petoskey stones would have more info then me.
I also have what you call 'soft Petoskey stones'. I know those cannot go in the tumbler or be hand polished. The book tells me just to put them in a pretty jar with some mineral oil. I was thinking about trying to spray just one of them with the lacquer and see what happens.
Mike, petrosky stone, as far as I know is a calcite. The coral it originates from has not gone mineral transfer. Of the few petrosky stones I have tumbled, I have so degraded the stone with all the polishes I was left with very little. A stone polisher I know, saves the final polish for the petosky stones after he cabs the original shape. He routinely mass final polished all his cabs I have never been able to final polish my cabs so I use a leather buff and cerium or tin oxide. I suggest if you have some choice samples, put them aside. Larimar is also similar. Do not tumble Larimar. If the only way I could polish petrosky stone was to tumble, I would do 220 for a few days, checking constantly. I would move up to 660 for a week, and run at least two weeks with cerium oxide. There might be some non mineralized organics trapped in the centers of the coral cells. Watch for gas build up. I once tumbled some fossilized buffalo scat and the tumbler had a soupy green mixture. There was no odor, but I suspect the mineralization was incomplete deep into the stones. It leached out with the tumble. Just my perspective on this. I often wondered if the reason the petrosky stone is localized to the Great Lakes region and not near ocean shores is the wave activity and the softness of the stone. If some seem agatized tumbling might work. Just keep a watch on it.
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hello its mike i just started my pre polish on my petoskey stones i did what you all said and that seams to work fine i left them in 14 houres with 300 then went to 400 ...14h. then 600. 14h. not done yet but they sure look prety good.... ;D thanks for all the help. ......mike
bigfoot: Finally getting up to speed, I hope!
Dec 14, 2014 19:01:41 GMT -5
1dave: Hi bigfoot, good to see you here! Show these good folks your horse head carvings!
Dec 14, 2014 21:25:33 GMT -5
Fossilman: Hurt my leg the other day on a roof,but still going to cut rocks today...Thumbs up
Dec 15, 2014 12:38:26 GMT -5
captbob: We seem to be missing a thread ...
Dec 15, 2014 23:42:42 GMT -5
rockpickerforever: I iz returned. Wascally wock hunt successful! A few fossils from OW; a little of everything, and a lot of palm bog agate from Indian Pass. 100+ lb boulder of yellow agate, sounded like glass when I rolled it up the hill, lol. Pics coming soon...
Dec 16, 2014 5:05:11 GMT -5
Fossilman: Jean SCORES!!!!! Cool beans and a thumbs up..............
Dec 16, 2014 11:07:11 GMT -5
Fossilman: Well rocks yesterday,woodworking today.Have a great day my friends!!
Dec 16, 2014 13:40:30 GMT -5
drocknut: Sorry you hurt your leg Fossilman. Welcome back you wrascally wock hunter. Looking forward to pics. Glad you had a successful hunt.
Dec 16, 2014 14:52:06 GMT -5
rockpickerforever: Thanks, Diane. If the weather cooperates, will get picks tomorrow. Mike, what did you hurt your leg fur? Thought you knew better than that! Hope it doesn't keep you down, and gets better soon.
Dec 16, 2014 16:06:31 GMT -5
Fossilman: No worries,it's getting better,will be doing the jig,soon....LOL
Dec 16, 2014 19:27:37 GMT -5
drocknut: Doing the jig is probably what hurt it in the first place. .lol
Dec 16, 2014 23:26:16 GMT -5
Fossilman: Falling off the ladder working on the church steeple did that-LOL............Caught myself before I hit the bottom of the ladder...Rolling eyes..
Dec 17, 2014 0:39:26 GMT -5
drocknut: Glad it wasn't worse
Dec 17, 2014 21:22:15 GMT -5
mtmadman: hey hey every body im baaaaaach
Dec 19, 2014 19:10:01 GMT -5
Fossilman: Oh oh Bob is back.....Where you at now buddy? Close to Montana are ya'.....?
Dec 19, 2014 21:53:43 GMT -5
drocknut: Welcome back
Dec 19, 2014 23:40:33 GMT -5
catmandewe: Good to see ya Bob!
Dec 20, 2014 11:47:11 GMT -5
adam: Agate hunters--woohoo!
Dec 20, 2014 18:48:13 GMT -5