Much loved mineral, in total (6)
I believe the answer is:
adored
'much loved' is the definition.
(I've seen this before)
'mineral in total' is the wordplay.
'mineral' becomes 'ore' (ore is a kind of mineral).
'in' means one lot of letters goes inside another.
'total' becomes 'add' ('add' can be a synonym of 'total').
'ore' going within 'add' is 'ADORED'.
(Other definitions for adored that I've seen before include "Really liked" , "Doted on" , "Deeply respected" , "Loved, venerated" , "Worshipped and venerated" .)