Valuable rocks (4)
I believe the answer is:
ores
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">valuable rocks</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ores that I've seen before include "Metal-bearing minerals" , "Mineral deposits" , "Bauxite, haematite etc" , "Rocks or minerals containing metals" , "Sources of metal" .)