What crystal growth habit can be compared to a cluster of grapes?

The crystal growth habit that can be compared to a cluster of grapes is botryoidal. This term is derived from "botryos," which is Greek for "bunch of grapes." Botryoidal growth results in rounded, bulbous forms that can resemble a mass of grapes, typically seen in minerals such as malachite and chalcedony. The smooth, rounded shapes of botryoidal specimens give them a distinguishable look that sets them apart from other crystal formations, making the comparison to a cluster of grapes quite fitting.

Other terms like boulder opal refer specifically to a type of opal found en masse within host rock, while brilliant cut pertains to a specific style of diamond cutting, neither of which describe a growth habit. Calcareous concretions denote sedimentary rock formations that have a different origin and structure compared to the rounded, agglomerated growth of botryoidal formations.