Cleavage is the tendency of a mineral to break along specific planes of weakness in its crystal structure. This is due to the arrangement of atoms within the mineral, creating planes where the bonds are weaker.

Basalt is an igneous rock, typically formed by the rapid cooling of lava. The minerals within basalt (like plagioclase feldspar, pyroxene, and olivine) are generally small and irregularly shaped, with no distinct crystallographic planes. This lack of defined crystal structure means there are no planes of weakness along which the rock will preferentially break.

Instead of cleavage, basalt typically fractures conchoidally, which means it breaks in smooth, curved surfaces resembling the inside of a shell.

Therefore, basalt does not have cleavage, and it is incorrect to refer to "basalt cleavage."