rubble -
The broken remains of an object, usually rock or masonry.
Wikipedia
Rubble is broken stone, of irregular size, shape and texture. This word is closely connected in derivation with "rubbish", which was formerly also applied to what we now call "rubble". Rubble naturally found in the soil is known also as 'brash'.
OmegaWiki Dictionary
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rubble The broken remains of an object, usually rock or masonry.