The Collaborative International Dictionary
Conchoidal \Con*choid"al\, a. [Cf. F. concho["i]dal.] (Min.) Having elevations or depressions in form like one half of a bivalve shell; -- applied principally to a surface produced by fracture.
Wiktionary
a. 1 (context mathematics English) Of or pertaining to a conchoid; that may be defined as a conchoid. 2 (context mineralogy of a fracture English) irregular, with planar, concentric curves, similar to those on a mussel shell. 3 (context mineralogy of a mineral English) That fractures with planar concentric curves (e.g., as flint, chert or obsidian).
Usage examples of "conchoidal".
Above you and around you are beams and joists, on some of which you may see, when the light is let in, the marks of the conchoidal clippings of the broadaxe, showing the rude way in which the timber was shaped as it came, full of sap, from the neighboring forest.
They passed a dense basalt sculpted with conchoidal fractures like the sides of elephants' skulls.