Powdery stuff - form of un-metal? (7)

I believe the answer is:

nutmeal

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'powdery stuff form of un-metal?' is the definition.
I can't judge whether this definition defines the answer.

'of un-metal?' is the wordplay.
'of' indicates anagramming the letters (the answer comes from or 'of' the letters).
'un'+'metal'='unmetal'
'unmetal' with letters rearranged gives 'NUTMEAL'.

Can you help me to learn more?

(Another definition for nutmeal that I've seen is " Gluten-free powder".)

I've seen this clue in The Independent.

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