Rang about alien rock (6)

I believe the answer is:

garnet

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'rock' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'rang about alien' is the wordplay.
'about' indicates anagramming the letters.
'alien' becomes 'et' (extra terrestrial).
'rang' with letters rearranged gives 'garn'.
'garn'+'et'='GARNET'

Can you help me to learn more?

(Other definitions for garnet that I've seen before include "Semi-precious stone of argent type" , "Deep red precious stone" , "Glassy red, yellow or green gemstone" , "Deep red gem stone" , "Deep red gemstone" .)

I've seen this clue in The Mirror.

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