Should not a magistrate be not merely the best administrator of the law, but the most crafty expounder of the chicanery of his profession, a steel probe to search hearts, a touchstone to try the gold which in each soul is mingled with more or less of alloy?
There are no more uses of "touchstone" in the book.
Show samples from other sources
"I’m not a good touchstone to use for judging your sanity."
Patrick Rothfuss -- The Name of the Wind
I considered Yamacraw a touchstone: if the Yamacraw children knew about it, then the chances were excellent that the vast majority of American children had been reached.