Solid lump of a precious metal (6)
I believe the answer is:
nugget
'solid lump of a precious metal' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nugget that I've seen before include "bit of treasure" , "Piece of gold, information" , "Scrap of information" , "Get gun to the lump" , "little wisdom?" .)