what is a touchstone in nethack
A Touchstone is one of several gray stones. It is used to identify gems by rubbing the gem on the stone. Rubbing an iron item on the touchstone will produce a signature scritch, scritch noise, which is the most reliable means of identifying the stone. Rubbing any gem on the touchstone will produce the same noise as the result if you are blind. A blessed touchstone will immediately identify the gem, as will an uncursed touchstone in the hands of an archeologist or gnome. An uncursed or cursed touchstone will merely distinguish glass from gems, but a cursed touchstone has a 1/5 chance of shattering gems that are rubbed on it. . A touchstone is always generated in the inventory of a jewelery shop's shopkeeper.