Regularly mined boron rocks that create pigment (5)
I believe the answer is:
ochre
'pigment' is the definition.
(ochre is a kind of pigment)
I don't understand how the rest of the clue works.
(Other definitions for ochre that I've seen before include "Light yellow-brown colour" , "What gives a yellow colour" , "Yellow-orange hue" , "Orange-yellow colour" , "Yellow/brown/red pigment" .)