His paper is turned to stone (8)
I believe the answer is:
sapphire
'to stone' is the definition.
(I've seen this before)
'his paper is turned' is the wordplay.
'is turned' is an anagram indicator.
'his'+'paper'='hispaper'
'hispaper' anagrammed gives 'SAPPHIRE'.
(Other definitions for sapphire that I've seen before include "Deep blue colour" , "Precious thing" , "precious item" , "Blue gem" , "His paper can be turned into a jewel" .)