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
mr.mohs: low nineties w/a hint of humidity and some good hot sauce
Jul 31, 2015 10:23:02 GMT -5
sHoTgUnNeR: 96 and rainy here. Miami hot. Yukky
Aug 1, 2015 8:17:20 GMT -5
drocknut: That is yucky Scott. Humidity makes it miserable.
Aug 1, 2015 9:09:59 GMT -5
sHoTgUnNeR: Indeed m'lady, indeed.
Aug 1, 2015 13:09:33 GMT -5
washingtonrocks: The Seattle area has reached the 90 degree mark for 11th time this year, "shattering" the old record from 1958 of 9 days lol. We don't know what to do with ourselves!
Aug 1, 2015 14:13:11 GMT -5
mr.mohs: downloading Win 10 @ 35% this is not very hot.... mostly™
Aug 1, 2015 14:17:48 GMT -5
washingtonrocks: mr.mohs, the forecast calls for tepid download times and torrential boredom.
Aug 1, 2015 14:24:30 GMT -5
mr.mohs: at this rate Win 11 will be out
Aug 1, 2015 15:00:18 GMT -5
jakesrocks: Hey Ed, give us a heads up about Win 10 after a few days. I still have time to cancel my order & stick with Win 7.
Aug 1, 2015 16:29:34 GMT -5
mr.mohs: will do! so far this is a 4 hour download. first download took 3 hours.. now it doing some updating with 87% to go... another hour, I suppose-- might have to send a message from the other side at this rate...mostly
Aug 1, 2015 18:03:38 GMT -5