Fruit character found under second rock (9)
I believe the answer is:
limestone
'rock' is the definition.
(I know that limestone is a type of rock)
'fruit character found under second' is the wordplay.
'fruit' becomes 'lime' (lime is a kind of fruit).
'character' becomes 'tone' (tone can mean a character or mood).
'found under' says to put letters next to each other.
'second' becomes 's' (common abbreviation).
'tone' after 's' is 'stone'.
'lime'+'stone'='LIMESTONE'
(Other definitions for limestone that I've seen before include "Basis of cement" , "Rock, basis for caves and pavements" , "Mineral" , "Hard calcium rock" , "building material" .)