firebrand vs lignite

firebrand

noun
  • A torch or other burning stick with a flame at one end. 

  • An argumentative troublemaker or revolutionary; one who agitates against the status quo. 

lignite

noun
  • A low-grade, brownish-black coal. 

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