Boring sample comprising carbon and rock (4)

I believe the answer is:

core

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'boring sample' is the definition.
'core' can be an answer for 'sample' (core is a kind of sample). I'm not sure about the 'boring' bit.

'carbon and rock' is the wordplay.
'carbon' becomes 'C' (chemical symbol).
'and' means one lot of letters go next to another.
'rock' becomes 'ore' (ores are found in rocks).
'c'+'ore'='CORE'

'comprising' is the link.

Can you help me to learn more?

(Other definitions for core that I've seen before include "Inmost part" , "Central part of the Earth" , "Central part of an apple" , "Centre, heart" , "Crux" .)

I've seen this clue in The Guardian.

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