Ship carrying quality jewels (6)
I believe the answer is:
stones
'jewels' is the definition.
'ship carrying quality' is the wordplay.
'ship' becomes 'ss'.
'carrying' indicates putting letters inside.
'quality' becomes 'tone' ('tone' can be a synonym of 'quality'**).
'ss' placed around 'tone' is 'STONES'.
(Other definitions for stones that I've seen before include "Small pieces of rock" , "''Sticks and ...... may break my bones''" , "Balls" , "Rolling rock group" , "Attacks" .)