A nonvesicular rock is made entirely of green 2-millimeter-diameter crystals that have a hardness of 6.5 and show fracture, but not cleavage. The rock is most likely

It is a kind of igneous rock known as Dunite

It has very high percentage (about 90%) of olivine, which is magnesium iron silicate. As the name suggest olivine (obtained from olive green) it is green in colour

Due to high percentage of this oliving in dunite rock it appears green in colour.

Also dunite rocks are ultramafic which means they have very low amount of silicates in them.

Dunite rocks are also characterized by no cleavage but presence of fracture in them.