Hard stone (5)
'hard stone' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for granite that I've seen before include "Constituent in Dartmoor" , "Very hard type of rock" , "Tangier (anag.)" , "A very hard rock from Tangier" , "Hard granular rock" .)
(Other definitions for agate that I've seen before include "Banded ornamental stone" , "Old drama critic" , "Semi-transparent stone" , "Striped stone" , "Precious stone" .)
'hard stone' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for flint that I've seen before include "Hard stone that sparks if struck against steel" , "Hard grey rock" , "Sparky mineral" , "It is used to produce sparks" , "used to start fire" .)