Steel-gray element (6)
I believe the answer is:
cobalt
'steel-gray element' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cobalt that I've seen before include "Magnetic-alloy element; a blue" , "Metal giving its name to type of deep blue" , "Metallic element, Co" , "kind of blue" , "Metallic element used in blue/green pigments" .)