What would grass and rock be together?

I am currently in the middle of writing a fictional fantasy/action/adventure book. In this book, the fighting forces each has a "nature type". The basic nature types are Earth (rock), Metal, Grass (plant), Fire, Water, Air, and Lightning. However, there are "fusion natures", where the character combines 2 natures and to make a new one. For example, Fire and Rock would make Lava. Metal and Lightning would make Laser. Water and Air would make Hurricane. I'm currently in a slump for what a fusion of grass and rock would be, any ideas?