Clay changed to this mineral in boxes (3)

I believe the answer is:

ali

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'clay' is the definition.
(Muhammad Ali was born Cassius Clay)

'this mineral in boxes' is the wordplay.
'boxes' indicates a hidden word (to box can mean to contain).
'ALI' can be found hidden inside 'this mineral in'.

'changed to' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for ali that I've seen before include "Mohammad . . ., . . . Hewson" , "US heavyweight boxer" , "Muhammad or Baba?" , "Muhammad ___ (or MacGraw?)" , "Person" .)

I've seen this clue in The Guardian.

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