Magnetite and malachite (4)
I believe the answer is:
ores
'magnetite and malachite' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ores that I've seen before include "Metal-bearing minerals" , "Sources of metal" , "Bauxite, haematite etc" , "Mined minerals" , "Mineral deposits" .)