A gem for each faint-hearted Dorothy (7)
I believe the answer is:
peridot
'a gem' is the definition.
(I know that peridot is a type of transparent gem)
'each faint-hearted dorothy' is the wordplay.
'each' becomes 'per' ('per' can mean for each).
'hearted' indicates the central letters.
'dorothy' becomes 'dot' (nickname for someone called Dorothy).
The middle letter of 'faint' is 'i'.
'per'+'i'+'dot'='PERIDOT'
'for' acts as a link.
(Other definitions for peridot that I've seen before include "Gemstone -- pre-do it (anag)" , "Top ride (anag) - gemstone" , "mineral" , "Gem" , "Pale green gemstone" .)