Hard metal element (7)
'hard metal element' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for iridium that I've seen before include "number 77" , "Silvery-white metallic element" , "Colourful compounds come from this" , "Hard metal element, Ir" , "Metallic element resistant to corrosion, atomic no. 77" .)
(Other definitions for tantalum that I've seen before include "Acid-resistant metal" , "Metallic element, symbol Ta" .)