speleothem vs stalactite

speleothem

noun
  • Any secondary mineral, deposited in a natural cave by the action of water. 

stalactite

noun
  • A secondary mineral deposit of calcium carbonate or another mineral, in shapes similar to icicles, that hangs from the roof of a cave. 

  • Coordinate term: stalagmite 

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