Gem, old, found by New York Times (4)
I believe the answer is:
onyx
'gem' is the definition.
(I know that onyx is a type of gem)
'old found by new york times' is the wordplay.
'old' becomes 'o' (abbreviation).
'found by' means one lot of letters go next to another.
'new york' becomes 'ny'.
'times' becomes 'x' (x resembles the multiplication or times sign).
'o'+'ny'+'x'='ONYX'
(Other definitions for onyx that I've seen before include "precious stone" , "Quartz used as a gem" , "Agate with different bands of colour" , "Black variety of quartz" , "Mineral with coloured layers" .)