noun
touchstone (assaying tool)
Literal mineralogical use: a dark siliceous stone used to test the purity of precious metals by the color of the streak left on it.
金の純度を調べるために試金石が使われた。
A touchstone was used to test the purity of the gold.
noun
touchstone; test; litmus test
Figurative use: a standard or criterion by which something is judged or recognized. Often used in phrases like 〜の試金石となる (serve as a touchstone for ...).
このプロジェクトは彼の能力の試金石となるだろう。
This project will serve as a touchstone of his ability.
選挙は政権への信頼を測る試金石だ。
The election is a litmus test of trust in the government.