conchoidal

adjective

1. (mathematics) Of or pertaining to a conchoid; that may be defined as a conchoid.

2. (mineralogy, of a fracture) Irregular, with planar, concentric curves, similar to those on a mussel shell.

3. (mineralogy, of a mineral ) That fractures with planar concentric curves (e.g., as flint, chert or obsidian).