Touch-stone, a hard black stone, occasionally used in assaying. The original kind was a peculiar bituminous quartz or flinty slate obtained from Lydia in Asia Minor, and hence known as Lydian Stone; but black basalt may be employed. The process is explained at ASSAYING, Vol. I. p. 507.
Touch-stone,
Chambers's Encyclopaedia, Volume 10: Swastika to Zyrianovsk and Index, p. 255
Source scan(s): p. 0274