It's an unusual material (5)

I believe the answer is:

satin

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

'material' is the definition.
(satin is a kind of material)

'it's an unusual' is the wordplay.
'it's an' anagrams to 'SATIN'.
Though, I'm not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for satin that I've seen before include "covered with?" , "Stain on shiny fabric" , "Material with glossy front and dull back" , "Stain found in cloth" , "Rich cloth" .)

I've seen this clue in The Globe and Mail.

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