Definition:
touchstone
- touchstoneA standard or criterion by which something is judged or recognized
- touchstoneA piece of fine-grained dark schist or jasper formerly used for testing alloys of gold by observing the color of the mark that they made on it
- touchstonea highly siliceous (usu black) stone or other stone for testing gold or silver by the colour of the mark each makes on it; (fig.) a criterion, a standard