Prattling 80s boy band rocks (7)

I believe the answer is:

gabbros

I'm a little stuck... Click here to teach me more about this clue!

'rocks' is the definition.
(gabbro is a kind of rock)

'prattling 80s boy band' is the wordplay.
I cannot quite see how this works, but
'80s' could be 's' and 's' is located in the answer.
'boy' could be 'ab' and 'ab' is present in the answer.
'band' could be 'o' (I've seen this in other clues) and 'o' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Times.

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