Cloth of precious diamonds (5)
I believe the answer is:
tweed
'cloth' is the definition.
(tweed is a kind of cloth)
'precious diamonds' is the wordplay.
'precious' becomes 'twee' (I've seen this before**).
'diamonds' becomes 'd' (abbreviation in bridge say).
'twee'+'d'='TWEED'
'of' acts as a link.
(Other definitions for tweed that I've seen before include "Harris cloth" , "Scottish and English river" , "passes between English and Scottish banks" , "Boundary river" , "Flow" .)