noun
Lydian stone; touchstone
Rare geological term for a type of siliceous rock historically used as a touchstone for testing precious metals. Mainly encountered in specialized literature.
硅板岩はかつて金の純度を調べる試金石として使われた。
Lydian stone was once used as a touchstone to test the purity of gold.
The term is composed of 硅 (silicon), 板 (board/slab), and 岩 (rock), reflecting its siliceous composition and slab-like appearance. The exact historical derivation is uncertain.