Ring encircling middle of spherical gem (5)
I believe the answer is:
pearl
'gem' is the definition.
(I know that pearl is a type of gem)
'ring encircling middle of spherical' is the wordplay.
'ring' becomes 'peal' (synonyms).
'encircling' indicates putting letters inside.
'middle of' says to take the centre.
The middle letter of 'spherical' is 'r'.
'peal' going around 'r' is 'PEARL'.
(Other definitions for pearl that I've seen before include "something highly valued" , "Precious gem" , "Lustrous structure in a mollusc shell" , "prized example" , "coming out of shell?" .)