ore vs rubble

ore

noun
  • Rock or other material that contains valuable or utilitarian materials; primarily a rock containing metals or gems for which it is typically mined and processed. 

rubble

noun
  • The broken remains of an object, usually rock or masonry. 

  • The whole of the bran of wheat before it is sorted into pollard, bran, etc.. 

  • A mass or stratum of fragments of rock lying under the alluvium and derived from the neighbouring rock. 

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