crack cocaine vs crack rock

crack cocaine

noun
  • A mixture of baking soda and cocaine in solid form that is smoked in a pipe as a narcotic. 

  • A mixture of salt substitute, ether, and cocaine in a semi-liquid form, which is far more potent than if made with baking soda alone. 

crack rock

noun
  • crack cocaine 

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