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.
In the beginning was the Floyd, and the Floyd was with Him, and He was with the Floyd. Syd Barret just disappeared, right after the happening. Lita Ford drives a suburban! Big Hair Heavy Metal is dead. Oh weeping and gnashing of teeth, the end is near. The answer is 42. 42! BING! BIG BING!
Follow the White Rabbit!
:)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
Fossilman: Went to the coast yesterday,it was 66 degrees down there-heaven for a half a day anyhow!! LOL
Jul 3, 2015 14:50:26 GMT -5
jakesrocks: In the mid 80's up here today. Wish the Canadians would keep their damned forest fire smoke up there. Only 3 miles visibility down here, and you can smell the smoke. Hmmmm, smells like Canadian bacon.
Jul 3, 2015 19:47:54 GMT -5
mr.mohs: pleasant summer Phoenix evenings all weekend long! Fireworks all over town. Lite it up !
Jul 3, 2015 21:27:12 GMT -5
snowmom: happy Independence Day USA Land of the Free Home of the Brave
Jul 4, 2015 5:02:27 GMT -5
Fossilman: Don,my boys live right next to the Canadian border,said it was pure nasty up there,no sun because of the smoke and haze and etc....You all need some strong eastern winds..
Jul 4, 2015 9:00:24 GMT -5
mr.mohs: stoking up the smoker right now
Jul 4, 2015 10:06:00 GMT -5
Fossilman: I will be right over Ed!!!!!
Jul 4, 2015 12:12:18 GMT -5
jakesrocks: Burgers & tater salad. Big ol' watermellon in the fridge cooling down, and a big ol' box of fireworks for tonight.
Jul 4, 2015 12:27:37 GMT -5
jakesrocks: Not as bad today Mike. Wind's out of the south east, blowing it away from us.
Jul 4, 2015 12:28:49 GMT -5
mr.mohs: messed up ! didn't get the crock pot of pinto's started in time. always tomorrow
Jul 4, 2015 12:47:22 GMT -5
woodman: Only 94.1 now, Had watermelon on patio under the trees laying in a hammock. Life is good! Happy 4th!
Jul 4, 2015 16:05:35 GMT -5
Rockoonz: Happy Independence Day. Went up the 5 to my home town and had breakfast with a high school classmate I haven't seen in over 40 years. Just had grilled pork chops and fixins, watermelon in a bit.
Jul 4, 2015 20:01:30 GMT -5
drocknut: Well, we got cooler weather today along with some rain. Glad I don't have to work today.
Jul 5, 2015 11:17:34 GMT -5
mr.mohs: I'm OFF everyday whether I have to work or not...mostly
Jul 5, 2015 12:55:28 GMT -5
jakesrocks: Had a danged unexpected thunder storm last night, just as it was getting dark enough to haul out the heavy artillery. Had to wait until after 11:00 PM to rattle some windows. Got all of the fireworks fired off just before round 2 of the storms rolled in.
Jul 5, 2015 13:02:15 GMT -5
jakesrocks: Saved one large mortar round for midnight New Years Eve.
Jul 5, 2015 13:04:00 GMT -5
mr.mohs: 2016 going come in w/a BOOM !!!
Jul 5, 2015 13:48:14 GMT -5