Thread: I Found It Over There

Originally Posted by bluesman7

eKretz, when you check with the file, is this on a small lapped area or on a fractured face? I'm assuming you are talking about checking rocks in the field before bringing them home.

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.