A mined extract of platinum (3)
I believe the answer is:
tin
'a mined extract' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'of platinum' is the wordplay.
'of' says the answer is hidden in the clue.
'TIN' is hidden in the letters of 'platinum'.
Can you help me to learn more?
(Other definitions for tin that I've seen before include "A silvery-white metal often in cans" , "Silvery white metal" , "Light metal" , "Kind of metal often used as food container" , "roofing material" .)