Mayamatam 33.13

33.13

ṭaṅkaghātādimṛdvīyā mandapakveṣṭakopamā
śilā bālā matā tajjñaiḥ sarvakarmasuninditā

That which is soft under chisel blows and resembles a half-baked brick / is considered by experts to be a child stone, censured in all works.