Crossword Genius

Fine fluffy stuff becoming very hard (5)

Ross

I believe the answer is:

flint

'very hard' is the definition.
(flint is a hard rock)

'fine fluffy stuff' is the wordplay.
'fine' becomes 'f' (abbreviation).
'fluffy stuff' becomes 'lint'.
'f'+'lint'='FLINT'

'becoming' is the link.

(Other definitions for flint that I've seen before include "Hard stone that sparks if struck against steel" , "Hard grey rock" , "Rock found in chalk" , "It is used to produce sparks" , "Hard kind of stone -- Welsh town on the Dee estuary" .)

I've seen this clue in The Independent.
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