Report of toughness in variety of rock (5)

I believe the answer is:

metal

I'm a little stuck... Click here to teach me more about this clue!

'rock' is the definition.
(I know that Metal is a type of metal music)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for metal that I've seen before include "Silver or gold, say" , "lead as one" , "Copper possibly" , "Element such as iron, copper, zinc etc" , "Maybe lead" .)

I've seen this clue in The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.