Having more weight applied to type of rock, say (6)
I believe the answer is:
bolder
'having more weight applied' is the definition.
(as in bolder text)
'type of rock say' is the wordplay.
'type of rock' becomes 'boulder'.
'say' indicates a 'sounds like' (homophone) clue.
'boulder' sounds like 'BOLDER'.
'to' is the link.
(Other definitions for bolder that I've seen before include "Braver or cheekier" , "Less shy" , "More impudent or daring" .)