Amorphous, cryptocrystalline, and crystalline materials can all present conchoidal fracture when they lack a preferential cleavage plane.
Cryptocrystalline silica, such as chert, or flint, with this material property were widely sought after, traded, and fashioned into sharp tools in the Stone Age.
Conchoidal fractures often result in a curved breakage surface that resembles the rippling, gradual curves of a mussel shell; the word "conchoid" is derived from the word for this animal (Ancient Greek: κογχοειδής konchoeidēs < κόγχη konchē).
[citation needed] Several subdefinitions exist, for instance on the Webmineral website:[4] In lithic stone tools, conchoidal fractures form the basis of flint knapping, since the shape of the broken surface is controlled only by the stresses applied, and not by some preferred orientation of the material.
This property also makes such fractures useful in engineering, since they provide a permanent record of the stress state at the time of failure.