Midlands town losing grand precious stone (4)
I believe the answer is:
ruby
'precious stone' is the definition.
(ruby is a kind of precious stone)
'midlands town losing grand' is the wordplay.
'midlands town' becomes 'rugby' (town in Warwickshire).
'losing' is a deletion indicator.
'grand' becomes 'g' ('G' can be a synonym of 'grand').
'rugby' with 'g' taken out is 'RUBY'.
(Other definitions for ruby that I've seen before include "Red precious stone" , "Deep red variety of corundum" , "Gemstone - shade of red" , "Deep 6 across" , "Jack perhaps" .)