July birthstone (9)
(Other definitions for cornelian that I've seen before include "gem" , "Gemstone" , "Dull red stone; lone cairn (anagram)" .)
'july birthstone' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ruby that I've seen before include "Precious red gem" , "Fortieth anniversary stone" , "Stony girl" , "Red precious stone" , "killed an assassin" .)