Pigment essentially etched into mineral aggregate (5)
I believe the answer is:
ochre
'pigment' is the definition.
(ochre is a colour)
'essentially etched into mineral aggregate' is the wordplay.
'essentially' says to take the centre.
'into' means one lot of letters goes inside another.
'mineral aggregate' becomes 'ore' (I've seen this before).
The middle of 'etched' is 'ch'.
'ch' going inside 'ore' is 'OCHRE'.
(Other definitions for ochre that I've seen before include "Earth-coloured pigment" , "Chore (anag) - pale brownish-yellow" , "Red or yellow pigment" , "Orangey colour" , "Earth coloured pigment" .)