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Post by Roller on Feb 18, 2010 19:05:14 GMT -5
 Hey guys .. I am about one year to this hobby now and have recently decided to start tumbling some of collected rocks from some different places that don"t do too much for me at the moment ..My problem is I really do not have any first hand experience with identifying the hardness.. I do have one of those mohs kits with a sample rock from each number 1 - 9 and glass and ceramic plate .. but even some of the rocks i rub on the plate do not leave a streak at all ... some do ...as far as the scrathcing goes ... I just dont know!!!! I will see powder and then wipe the rock clean and then see nothing .which means something is definately be scratched. even under 10 x i dont see a scratch though depending on the rock or color as well ..xls seem much easier to tell but i dont wanna ruin ..Any good hints or tips will be very much appreciated ... Also does any one use the hardness pick set and does that make things a whole lot easier .. I have a feeling it does !!!!!! Greg Thanks |
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rallyrocks
fully equipped rock polisher
Member since November 2005
Posts: 1,507
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Post by rallyrocks on Feb 18, 2010 19:43:47 GMT -5
If you rub a rock on the plate and it doesn't leave a streak, it is probably harder than 6-7.
If there is not a scratch left in the surface of a stone after a scratch test, it is probably harder than the control you did the scratch with, so try a harder one and see if that leaves a mark.
Thing about Mohs hardness is that it is not absolute- it is just a relative scale, so when things are close to each other it can be hard to get definitive answers as to which is harder, but the good thing is that "close" is usually "good enough" when sorting rocks for tumbling.
Anything softer than 4.5 probably shouldn't be tumbled, and certainly anything that soft should only go with material that is the same hardness, but anything in the range of 5-6 is usually OK together, as is 6-7 or even 7-8, but I'd try not to mix anything that is 2 or more points apart in hardness, so don't put a 7 in with a 5 or a 5 in with a batch of 8's, and you should be fine.
I generally don't pay much attention to hardness unless I am trying to ID a stone and even then, it's only a rough idea, since chemical or spectral analysis is really the only true way to know for sure.
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Post by susand24224 on Feb 18, 2010 22:27:29 GMT -5
If you mix stones of different hardnesses together tumbling, at least in a rotary, it may not be that much of a problem. It is true, as said before, that you should *try* not to do that. But--after the first tumble together in 60/90 grit (or 80) you will see some stones wearing down quickly and others not as affected. This will help you with hardness. You will also see other subtle differences in the way the rocks react to the tumbling process.
Harder rocks will "beat up" on softer ones, but it has been my experience that in the first stages of tumbling, the problem is minimal. There are a few exceptions to this, but in general the softer ones are salvagable.
Now polishing is a different story. The softer ones simply won't polish. You can always set them aside and when you have enough softer ones, give them their own, private polish.
Many, many times (particularly when I can't find my glasses) I have accidentally put a softer rock in with harder ones and rarely have I destroyed the softer ones. So, unless you have a really special rock, my theory is go ahead and tumble and sort as you go--the worst that will happen is that you will fracture or lose a rock along the way.
If your rock is too soft to tumble well, it will disintegrate pretty much regardless of what you do. Again, there are exceptions--with such things as malachite and its cousins, you can tumble with tons of cushion and get reasonable results and a Mohs 7, for example, could destroy the softer ones. These rocks are *obviously* much softer, though.
I don't have much experience with vibes, so if that is what you are using, please ignore this!
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Post by johnjsgems on Feb 18, 2010 23:59:50 GMT -5
What Rallyrocks said. If you scratch a rock with a knife blade it is too soft. If the knife leaves a line that rubs off with finger it is harder than the steel and should be hard enough to polish.
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Hey guys .. I am about one year to this hobby now and have recently decided to start tumbling some of collected rocks from some different places that don"t do too much for me at the moment ..My problem is I really do not have any first hand experience with identifying the hardness.. I do have one of those mohs kits with a sample rock from each number 1 - 9 and glass and ceramic plate .. but even some of the rocks i rub on the plate do not leave a streak at all ... some do ...as far as the scrathcing goes ... I just dont know!!!! I will see powder and then wipe the rock clean and then see nothing .which means something is definately be scratched. even under 10 x i dont see a scratch though depending on the rock or color as well ..xls seem much easier to tell but i dont wanna ruin ..Any good hints or tips will be very much appreciated ... Also does any one use the hardness pick set and does that make things a whole lot easier .. I have a feeling it does !!!!!! Greg Thanks 
