Work with aluminium and stone (4)
I believe the answer is:
opal
'stone' is the definition.
(gemstone)
'work with aluminium' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'with' means one lot of letters go next to another.
'aluminium' becomes 'al' (Al is the chemical symbol for aluminium).
'op'+'al'='OPAL'
'and' acts as a link.
(Other definitions for opal that I've seen before include "Delicately-coloured gem" , "what may be set in 29 [DIAL]" , "Mineral used as a gemstone, of hydrated silica" , "Glassy gemstone" , "Milky white gemstone" .)