which stone is more resilient to the strings?
How thick?
I have a couple riends hounding me to make a few.
In my experience, jasper is the most resilient. Fewer fractures and a Mohs hardness of 7 seem to provide a nice "sharp" tone on the strings. Plastic/Nylon picks are duller sounding. On the negative side, the "stone" picks tend to be noisier than a plastic pick when they pass along a string. Also, they can also be slippery when wet from sweat. I am working on trying some transparent material that can be applied to increase friction in the finger contact area. Some guitar players love them and some hate them.
For their look, they are unlike anything around. Pick collectors love them and they make great gifts for guitar playing family and friends.
The best material I have found is either Quartz or Rose Amethyst. They can make an acoustic guitar sound wonderful but they tend to have fractures which means, of course, that they can break with too much finger pressure.
For guitar players, I shoot for a thickness between 1.8 - 2.5mm thick. Plastic picks are really thin (about .68mm for a medium pick) so the thicker picks can take a little getting used to.
For bass guitar, anywhere from 2 - 3.5. I have produced some for bass that are 4.5mm at the top but I taper them to 2.5mm at the tip.
Edges can be either fairly sharp or rounded. Shapes can vary from tear drop to a wide offset to just a standard size, depending in the player's preference.
Let me know if you have any other questions. People have been very helpful to me here so I want to return the favor.
I tend to put a fairly sharp point on mine and I tell people they shouldn't "windmill" like Pete Townsend of The Who while playing their $5000 guitar because they can easily damage the wood. Used properly, they will last a very long time.