Crossword Genius

Beach pebble or rock (9)

Ross

I believe the answer is:

sandstone

'rock' is the definition.
(sandstone is a kind of rock)

'beach pebble' is the wordplay.
'beach' becomes 'sand'.
'pebble' becomes 'stone' (I've seen this before).
'sand'+'stone'='SANDSTONE'

'or' acts as a link.

(Other definitions for sandstone that I've seen before include "Such building material" , "Type of sedimentary rock" , "Rock containing quartz grains" , "Among the best of building materials" .)

I've seen this clue in The Guardian.
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