TOADSTONE
Etymology
Noun
toadstone (countable and uncountable, plural toadstones)
A small stone, once believed to be a jewel embedded in the head of a toad, worn as an amulet.
(geology) A soft, earthy variety of trap-rock of a brownish-grey colour, looking like an argillaceous deposit.
Source: Wiktionary
Toad"stone`, n.
1. (Min.)
Definition: A local name for the igneous rocks of Derbyshire, England; --
said by some to be derived from the German todter stein, meaning dead
stone, that is, stone which contains no ores.
2. Bufonite, formerly regarded as a precious stone, and worn as a
jewel. See Bufonite.
Source: Webster’s Unabridged Dictionary 1913 Edition