amulet vs madstone

amulet

noun
  • A kind of protective charm or ornament, often bearing magical symbols, worn for protection against ill will, negative influences, or evil spirits. 

madstone

noun
  • A stone believed to have the power to heal the bite of a rabid or venomous animal. 

How often have the words amulet and madstone occurred in a corpus of books? (source: Google Ngram Viewer )