tumblefly
off to a rocking start
Member since September 2022
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Post by tumblefly on Oct 10, 2022 9:57:06 GMT -5
I've been tumbling a 6lb run of crazy lace agate for about a month now, and enough wore down last week that I had space to fill - so I threw in a couple of rough Botswana agates, figuring they would be the same hardness. But WOW - a week later, and the Botswana agates have worn away almost to half their original size, while the crazy lace looks barely any different from the week before. This is all stage 1, 60/90 grit.
I've googled both agates and they both come back as 6.5-7 on the Mohs - any ideas why the BAs would wear so quickly and almost no changes took place on the CLAs?
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vance71975
freely admits to licking rocks
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Post by vance71975 on Oct 10, 2022 11:35:00 GMT -5
I've been tumbling a 6lb run of crazy lace agate for about a month now, and enough wore down last week that I had space to fill - so I threw in a couple of rough Botswana agates, figuring they would be the same hardness. But WOW - a week later, and the Botswana agates have worn away almost to half their original size, while the crazy lace looks barely any different from the week before. This is all stage 1, 60/90 grit. I've googled both agates and they both come back as 6.5-7 on the Mohs - any ideas why the BAs would wear so quickly and almost no changes took place on the CLAs? One thing I have learned is that hardness isnt linear and 2 stones of the same hardness can cut at very differnet rates. Quartz for example is a 7 on the mohs scale, same as Lace agate, but my quartz what smooth at 7 days where as my lace agate isnt even 100% smooth after 21 days. I think the reason for this is the Mohs scale was created for Minerals. "Testing the hardness of rocks is less effective than testing the hardness of minerals. A rock is basically a mixture of various minerals, although it can contain non-mineral materials such as natural glass and fossils. (Fossils aren't minerals because they are organic, while glass isn't a mineral because it lacks an internal crystalline structure). Let's take a granite pegmatite for example. This might contain grains of topaz (H= 8), quartz (H=7), feldspars (H=6) and muscovite mica (H= 2.5). You could thus get a range of hardness depending on which grain you tested. In a coarse grained rock, identifying the individual minerals allows you to identify the rock. If the rock is fine-grained, it's harder to interpret the results." www.mindat.org/article.php/1925/Mohs%27+hardness+testing+of+minerals+and+rocks
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brybry
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Post by brybry on Oct 10, 2022 13:44:34 GMT -5
I've been grinding & tumbling Bots since last year. It's taken this long because of how hard they are. I do find one or 2 with a soft, rotten spot but it's been less than 5 out of 26lbs.
Either yours were rotten to begin with or they weren't Bots to begin with.
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tumblefly
off to a rocking start
Member since September 2022
Posts: 3
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Post by tumblefly on Oct 10, 2022 17:05:35 GMT -5
Vance - that sounds like it might be it. I'm guessing the "outer shell" of the Botswana agates must have been softer than the inside glassier part, as that's what's been grinded off for the most part.
Brybry - as far as I can tell, they're the real deal... got them from The Rock Shed and would be surprised if they'd mislabeled them.
Thanks!
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vance71975
freely admits to licking rocks
Member since September 2022
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Post by vance71975 on Oct 10, 2022 17:21:12 GMT -5
Vance - that sounds like it might be it. I'm guessing the "outer shell" of the Botswana agates must have been softer than the inside glassier part, as that's what's been grinded off for the most part. Brybry - as far as I can tell, they're the real deal... got them from The Rock Shed and would be surprised if they'd mislabeled them. Thanks! Some Info I just got from Mindat cause I asked about hardness. Mindat is a resource that a Geologist suggested to me, its Geologists,gemeologists, etc its an educator resource and has a lot of professional experts. Great site for double and triple checking when you are not sure on a rock. "There is hardness and there is tenacity ("toughness"). Quartz crystals are hard but brittle, whereas chalcedony like agate is a composite material made of myriads of tiny intergrown crystals that is quite tough. Agate can take a blow more easily than a quartz crystal because the mechanical forces are dispersed in the composite matter, while a crystal behaves more like glass. One can really feel this when cutting quartz and agate with a saw: It is much easier to cut quartz crystals." "Agate is composed of interlocking micro crystals and is quite tough. Quartz (clear/rose etc.) is composed of larger macro crystals and is more easily smoothed by an abrasive that is harder than they both are. Even diamond abrasives will slow down on agate." "A quick note about the Mohs Hardness scale. It is a field test for determining relative hardness between mineral species & while comparative & very useful in relative observations, it is not all that precise. So two specimens may have a Mohs hardness of 7, but still have a slightly different hardness from each other. That may be part of what you are seeing." Another good example I found was Diamond vs copper, diamond is a 10 hardness but if you smack it with a hammer it will shatter where as copper is a 3 but if you smack it with a hammer it will just smoosh some. So if I am gathering correctly I have learned the following. 1) Mohs scale is best for pure mineral samples and slightly less useful for the rocks most of us are tumbling. 2) Mohs is limited to Strictly Hardness and tells nothing about how fast or slow something will tumble. 3) We need a Lapidary scale that is more accurate for lapidary than the mohs scale lol
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brybry
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Post by brybry on Oct 10, 2022 18:55:35 GMT -5
Vance - that sounds like it might be it. I'm guessing the "outer shell" of the Botswana agates must have been softer than the inside glassier part, as that's what's been grinded off for the most part. Brybry - as far as I can tell, they're the real deal... got them from The Rock Shed and would be surprised if they'd mislabeled them. Thanks! That explains a lot. The Bots I got already had the outer rind off. If I remember correctly, the ones from the Rock Shed still have quite a bit of the rind still on them. That's why you noticed the extreme size change. Now that the rind is off or mostly off, you'll discover the joys of a months long grind
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