sford13
starting to spend too much on rocks
Member since September 2009
Posts: 119 
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Post by sford13 on Mar 25, 2010 9:32:00 GMT -5
So when you are looking at material that you are not sure of an identity how do you determine if it is even worth the time to go into the tumbler. Is the pocket knife scratch test a pretty good rule of thumb? Meaning if it can't be scratched by the knife give it a try. If it is scratched toss it. I have too many rocks and not enough time to give a rock that will never shine time in one of my tumblers.
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Post by deb193redux on Mar 25, 2010 11:02:53 GMT -5
I would add a few more scratches. You can readily get a quartz point. A single crystal of quartz, terminated by a point.
If it is between the nail (MOHS 5) and the point (MOHS 7), use the recipie for softer stone.
If it is above the quartz point, use the grit sequence (and patience) for harder stones, e.g., rubies.
You can also get something closet to MOHS 6. Or you could take a broken cab of something softer like obsidian instead of finding somethign exactly MOHS 6.
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Post by johnjsgems on Mar 25, 2010 11:36:26 GMT -5
Scratch tests are good for a start. If you collect your own rough a rock hammer is useful. Chip a surface (or observe fresh, unweathered surfaces). Agates/jaspers will be smooth and almost shiny. Water will bead up on the surface or run off. Porous jasper will soak up water and never polish. It will usually be rough/pitted on surface. Crappy jasper won't scratch either. A lot of softer rocks will feel lighter too. Some of these things are learned through experience.
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chromenut
fully equipped rock polisher
Member since December 2009
Posts: 1,971
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Post by chromenut on Mar 26, 2010 20:48:46 GMT -5
Really good info here...
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Post by Jack ( Yorkshire) on Mar 28, 2010 8:22:24 GMT -5
Beach Rocks
I Use a knife if it leaves a slaty grey mark on the stone it will polish
If its a chalky mark or scratch it wont or isent worth the trouble
Jack
Yorkshire UK
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revco
starting to spend too much on rocks
Another Victim Of The Rockcycle
Member since February 2010
Posts: 162
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Post by revco on Apr 1, 2010 13:41:01 GMT -5
I'm currently in the process of refining my hardness tests, thanks to information I've found here and elsewhere. I collect my own rock and I'm trying to get to a place where I can be fairly confident that all my tumbles are within one hardness point of each other.
What I've decided to try is to use a piece of sharp glass (MOHS 5.5) to determine hard or soft.
For hard, I'll then use a piece of quartz (MOHS 7) to determine if it's below 7 or above. If it's above, I'll use sandpaper (MOHS 8) - if it scratches, it's between 7 and 8, if not, it's 9 or above. If the quartz scratches it, then I'll use a steel file (MOHS 6.5) - if it scratches, then it's between 5.5 and 6.5 - if not, then it's between 6.5 and 7. From my research and experience, a lot of rocks are between 6.5 and 7...so that's a "category" for me.
For soft, I'll use an iron nail (MOHS 4) to determine if it's from 4 to 5.5 or below. Though not very useful for tumbling, you could then use a penny (MOHS 3) to determine if it's from 3 to 4. Though I haven't done much soft material polishing, I do know that flourite is around MOHS 4 and will take a shine.
I've also decided to try and move my hardness testing between 60/90 and 120/220. I've found that a mixed tumble in course is usually not problematic with pellets, so long as you're checking the barrel every 5 or 6 days. I've yet to test this method, but I'm hoping the 120/220 will remove any scratches from my testing efforts. The reason for this is that I've had somewhat inaccurate results with rough rock - maybe it's the matrix or the weathering, but it hasn't been solid for me. If I don't have a large sample, it's often not desirable to break apart the rock for a fresh surface.
That's my 2 cents on the subject.
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