Can't be broken? A mother with worker in Evans Head? (10)

I believe the answer is:

adamantine

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'can't be broken?' is the definition.
I can't tell whether this defines the answer.

'a mother with worker in evans head?' is the wordplay.
'mother' becomes 'dam' (female parent of an animal).
'with' says to put letters next to each other.
'worker' becomes 'ant' (worker is a type of ant).
'head?' indicates taking the first letters (I've seen 'head of' mean this).
The initial letter of 'evans' is 'e'.
'a'+'dam'+'ant'+'in'+'e'='ADAMANTINE'

Can you help me to learn more?

(Other definitions for adamantine that I've seen before include "attractive" , "Unbreakable" , "firm" , "Impervious to pleas" , "very strong" .)

I've seen this clue in the Sydney Morning Herald.

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