RhymeZone: conchoidal definitions

Definitions of conchoidal:

adjective: (mathematics) Of or pertaining to a conchoid; that may be defined as a conchoid.
adjective: (mineralogy, of a fracture) Irregular, with planar, concentric curves, similar to those on a mussel shell.
adjective: (mineralogy, of a mineral) That fractures with planar concentric curves (e.g., as flint, chert or obsidian).

(Definitions from Wiktionary)