Definition of "greenstone"

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

(New Zealand) 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)  examples