Maybe a ruby from curmudgeon sorry after Georgia’s left (8)

I believe the answer is:

corundum

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'maybe a' is the definition.
I can't tell whether this defines the answer.

'ruby from curmudgeon sorry after georgia's left' is the wordplay.
'ruby' becomes 'gem' (ruby is an example).
'from' suggests deleting specific letters.
'sorry' indicates anagramming the letters (sorry can mean poor-quality or wretched).
'after georgia's left' becomes 'm' (I can't justify this - if you can you should give a lot more credence to this answer).
'curmudgeon' with 'gem' taken out is 'curudon'.
'curudon' anagrammed gives 'corundu'.
'corundu'+'m'='CORUNDUM'

Can you help me to learn more?

(Other definitions for corundum that I've seen before include "Extremely hard mineral used as an abrasive" , "Abrasive form of alumina" , "Stone" , "Hard form of alumina" .)

I've seen this clue in The Independent.

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