Weighty and large stones (6)
I believe the answer is:
gravel
'stones' is the definition.
(I've seen this before)
'weighty and large' is the wordplay.
'weighty' becomes 'grave' (I've seen this in another clue).
'and' means one lot of letters go next to another.
'large' becomes 'L' (eg in clothes sizes).
'grave'+'l'='GRAVEL'
(Other definitions for gravel that I've seen before include "Small stones for surfacing driveways" , "Stone mixture for paths" , "Shingle" , "bits of rock" , "Small rounded stones" .)