Tag with key material=* to indicate some kind of metal.
Other materials at Template:Map Features:material.
Possible tagging mistakes
material=Metal🔎 ‒ Capitalized
material=metallo🔎 ‒ Generally a misspelling or a different language
material=Metallo🔎 ‒ Generally a misspelling or a different language
material=metall🔎 ‒ Generally a misspelling or a different language
material=Metall🔎 ‒ Generally a misspelling or a different language
material=métal🔎 ‒ Generally a misspelling or a different language
material=Métal🔎 ‒ Generally a misspelling or a different language
material=métallique🔎 ‒ Generally a misspelling or a different language
material=Métallique🔎 ‒ Generally a misspelling or a different language
Combined values should use ";". A few samples:
material=wood+metal🔎 ‒ should be "wood;metal"
material=wood and metal🔎 ‒ should be "wood;metal"
material=wood; metal🔎 ‒ should be "wood;metal"
material=wood,metal🔎 ‒ should be "wood;metal"
material=wood, metal🔎 ‒ should be "wood;metal"