greenstone vs nephrite

greenstone

noun
  • pounamu, the green-hued minerals of New Zealand used by Māori to make tools, ornaments and weapons (any of three varieties of nephrite jade or one variety of bowenite) 

  • any of several green-hued minerals used for making various artefacts in early Mesoamerican cultures, e.g. greenschist, chlorastrolite, serpentine, omphacite, or chrysoprase 

nephrite

noun
  • A semi-precious stone, one of the two types of stone commonly referred to as jade (the other being jadeite). 

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