touchstone

[ tuhch-stohn ]
/ ˈtʌtʃˌstoʊn /

noun

a test or criterion for the qualities of a thing.
a black siliceous stone formerly used to test the purity of gold and silver by the color of the streak produced on it by rubbing it with either metal.

Origin of touchstone

First recorded in 1475–85; touch + stone

Example sentences from the Web for touchstone

British Dictionary definitions for touchstone

touchstone
/ (ˈtʌtʃˌstəʊn) /

noun

a criterion or standard by which judgment is made
a hard dark siliceous stone, such as basalt or jasper, that is used to test the quality of gold and silver from the colour of the streak they produce on it