Guitar Picks made of stone are quite rare and therefore there isn't much material on them.
The process of making a Guitar Pick out of a rock specimen is tedious and long, very much like the making of a cabochon which is a slice of rock cut to shape and polished by hand over and over again (10-15 stages of polishing) until it is mirror smooth and ready to be set inside a silver or gold frame to make a most special and beautiful looking piece of jewelry. While natural flaws in the stone are acceptable when it is a cabochon, in case of a guitar pick it makes it unusable if the flaw happens to be on the edges of the pick.
20%-50% (and sometimes more) of the picks are being disqualified on our QC at the end of the making process. This fact is strongly affected by the characteristics of the rock which the picks are cut from.