Bit of quartz includes metal (4)
I believe the answer is:
zinc
'metal' is the definition.
(zinc is a metal)
'bit of quartz includes' is the wordplay.
'bit of' indicates the answer is hidden within the clue.
'ZINC' is hidden in the letters of 'quartz includes'.
(Other definitions for zinc that I've seen before include "Penultimate element (alpha. order)" , "Metal used in brass" , "Silvery-white metal" , "Galvanizing metal" , "Metal, Zn" .)