Semi-precious stone, one stored in unusual red pot (7)
I believe the answer is:
peridot
'semi-precious stone' is the definition.
(I've seen this before)
'one stored in unusual red pot' is the wordplay.
'one' becomes 'I' (Roman numeral).
'stored in' indicates putting letters inside.
'unusual' is an anagram indicator.
'red'+'pot'='redpot'
'redpot' with letters rearranged gives 'perdot'.
'i' inserted into 'perdot' is 'PERIDOT'.
(Other definitions for peridot that I've seen before include "Top ride (anag) - gemstone" , "Pale green gemstone" , "olivine" , "I deport (anag) - gemstone" , "Gemstone -- pre-do it (anag)" .)