Mineral, only without large cross (4)
I believe the answer is:
onyx
'mineral' is the definition.
(onyx is a kind of mineral)
'only without large cross' is the wordplay.
'without' indicates named letters should be taken away.
'large' becomes 'l'.
'cross' becomes 'x'.
'only' with 'l' removed is 'ony'.
'ony'+'x'='ONYX'
(Other definitions for onyx that I've seen before include "Agate with different layers of colour" , "Banded gemstone" , "precious stone" , "Smooth stone with bands of colour" , "Form of agate" .)