conchoidal

Adjective

conchoidal (comparative more conchoidal, superlative most conchoidal)

1. Of or pertaining to a conchoid; that may be defined as a conchoid.
   • […] a conchoidal hyperbola with an oval at its convexity.c. 1695, Isaac Newton, 1976, D. T. Whiteside (editor), The Mathematical Papers of Isaac Newton, Volume 7: 1691-1695, page 621
2. Irregular, with planar, concentric curves, similar to those on a mussel shell.
   • It is distinguished by its splendent lustre and conchoidal fracture.1821, Coal, entry in Andrew Ure, A Dictionary of Chemistry on the Basis of Mr Nicholson's, unnumbered page
   • Some flakes detached in a controlled manner have characteristics of conchoidal fracture.2005, “Chapter 19: Lithic Studies”, in Herbert D. G. Maschner, Christopher Chippindale, editors, Handbook of Archaeological Methods, volume 1, page 719
3. That fractures with planar concentric curves (e.g., as flint, chert or obsidian).
   • The customary transitions of pitchstone are, into Chalcedony, Chert, Semi-opal; also into a substance resembling conchoidal shining jasper, found in clay strata, entangled in trap, or volcanic rock; and lastly, into Trap.1821, Focus of Philosophy, Science and Art, Volume 1, Issues 1-4, page 74