conchoidal Syllabification: (con·choi·dal)Pronunciation: /käNGˈkoidl/Definition of conchoidal adjective chiefly Mineralogy denoting a type of fracture in a solid (such as flint or quartz) that results in a smooth rounded surface resembling the shape of a scallop shell. conchoidal in other Oxford dictionaries Definition of conchoidal in the British & World English dictionary