toadstone
nounEtymology From toad + stone.
1
A small stone, once believed to be a jewel embedded in the head of a toad, worn as an amulet.
2
Geography, Geology, Natural sciences A soft, earthy variety of trap-rock of a brownish-grey colour, looking like an argillaceous deposit.
- Rowley-Rag appeared to be the same thing as basalt and toadstone resembled some species of lava.2004, Robert E Schofield, The Enlightened Joseph Priestley, Pennsylvania State University, published 2004, page 162: