"Sweet are the uses of adversity,
Which, like the toad, ugly and venomous,
Wears yet a precious jewel in his head."
April 23, 1564, birthday of William Shakespeare. In his "As You Like It" he mentions "toadstones."
Toadstones or Bufonites are gemstones growing in the head of a living toad. The stone must be recovered by putting the toad on a red blanket or by exposing the animal to heat - the animal will then spit out the stone.
Despite the vague descriptions that exist for this supposed gemstone, "toadstones" were identified by some scholars as the fossilized teeth of Lepidotus - an extinct genus of ray-finned fish from the Jurassic and Cretaceous periods - probably as the round shape and smooth surface of the fossil teeth resemble the eyes of a toad.