One of the three main types of rock (7)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
igneous
(Other definitions for igneous that I've seen before include "Like fire - type of rock" , "Category of rock, being of solidified molten magma" , "Of fire, fiery" , "(Of rock) originating in molten state" , "Formed of solidified magma" .)