Ore of lead (6)
I believe the answer is:
'ore of lead' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for galena that I've seen before include "Commonest ore of lead - Angle "A" (anag)" , "Lead sulphide mineral" , "Len, GAA produces lead sulphide" , "Angela (anag) - ore producing lead" .)