Get rid of old china stone (4,4)

I believe the answer is:

fire opal

'stone' is the definition.
The definition and answer can be both substances as well as being singular nouns.
Perhaps you can see a link between them that I can't see?

'get rid of old china' is the wordplay.
'get rid of' becomes 'fire' (as in firing from a job).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'china' becomes 'pal' (I've seen this before).
'fire'+'o'+'pal'='FIRE-OPAL'

(Another definition for fire opal that I've seen is " gemstone".)

I've seen this clue in The Guardian.

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