Picture from a different thread but I use a Sharpie!:D
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Picture from a different thread but I use a Sharpie!:D
Attachment 186608
That is one of the issues with hard rock is that it is very hard to work with. Rock that separates into layer like you described is often slate or shale. One of the issues I have here is that the shale is too badly fractured to be able to work with most of it. The slate is a little easier but often has gas bubbles in it. However if you can find a good layer they both have the potential of great hones.
My father passed on some stones he had collected to me and my wife. She made notes etc. to put in the box's. The shelf they were on collapsed under the weight and all the notes got mixed up......:cry:
there is no cry button. Sad story about the rocks and notes.
Wow that sucks about the notes.
Well I have to recant on the file. I realized I was testing with a cheap Cobalt file. Not so much luck with a Smith file. I will keep messing with these to see what they will do.
If I am uncertain I test with an old knife with a wide bevel.
I check on a small lapped area. If you check just on the rough stone you can get some idea if it will cut steel but it won't give you a very good indication of cutting speed or finish. Over time you'll get a better idea of what stones to look closer at. Sometimes the sparkle will indicate a stone that will cut steel and sometimes not. Sometimes a stone without any sparkles will work great. My Jnat for instance doesn't have any that I can see and it cuts like crazy.
Conchoidal fracture can be found in stone beside novaculite - flint, obsidian, quartzite and a couple others. The main thing is most of the rocks that fracture this way are very high in silica. Novaculite for instance is like 99.6+%, quartzite ranges from the low to high 90's percentile. Another good field check is to break off a chunk and check the grain size - finer stones will usually be finer grained on the fractured surface, but you'll need to get more familiar with seeing different stones to get an idea what that even looks like.
I don't like to check with a knife personally because they are usually not as hard as a razor - a stone that will cut a quality file will cut anything, where a stone that might cut a softer knife may not cut the file or a razor. If you have a knife of known hardness that is 60+ Rc then that is different though. Shaun knows his stuff so I'm sure he has it handled.
Will do......if I ever get the damn thing lapped.