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Of, relating to, or being a surface characterized by smooth, shell-like convexities and concavities, as on fractured obsidian.

[From Greek konkhoeidēs, mussellike : konkho-, concho- + -oeidēs, -oid.]

con·choi′dal·ly adv.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


1. (Geological Science) (of the fracture of minerals and rocks) having smooth shell-shaped convex and concave surfaces
2. (Geological Science) (of minerals and rocks, such as flint) having such a fracture
conˈchoidally adv
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(kɒŋˈkɔɪd l)

denoting a fracture shape whose surface resembles the inside of a clamshell, characteristic of certain minerals.
con•choi′dal•ly, adv.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
References in periodicals archive ?
Conchoidal features of various sizes (Figs 5, 6I), along with straight and arcuate steps (Figs 5, 6J) and parallel striations (Figs 5, 6K), occur on angular and sometimes on subangular grains.
Arrow 2 points to the conchoidal fracturing of chert.
The prisms appear to lack internal subunits and fractures through individual prisms are conchoidal rather than along specific planes.
Solid gallium has an orthorhombic crystal structure and displays a conchoidal fracture similar to glass.
The bitumen observed on the core DS1 was described as hard, brittle, steel-gray, insoluble in chloroform, conchoidal fracture, and nonfluorescent.
While the flakes share characteristics - such as sharp edges and conchoidal fractures - with hominin stone tools, they are not used as such by the monkeys.
It was opaque black with a vitreous lustre and a surface that showed conchoidal fracture patterns.
Essa rocha, que apresenta diferentes graus de friabilidade, e formada por areias de diferente granularidade que podem se encontrar cimentadas por processos diversos, as vezes por um cimento silicoso (arenito silicificado), outras por se encontrar em intercalacoes com o basalto da Formacao Serra Geral, situacao na qual se forma um quartzito de fratura conchoidal (INSUGEO 2007; Grupo Consultor Mesopotamico 2006-2009; Remesal y Chavez 2014).
Silcretes are brittle, often with a lustrous conchoidal fracture, and very resistant to weathering.
In addition, black, fine-grained, conchoidal rocks are common in archaeological contexts in the Mackenzie Valley, and qualitative visual comparison of rock types is susceptible to observer error (cf.
For example, in the melting of steel, an aluminum content of 0.06% maximum may be satisfactory for one part, while another part requires 0.03% maximum aluminum content to avoid conchoidal fracture of the test specimens.
FRACTURE SCALE: l=premature(planar)fracture; 2=uneven; 3=poor conchoidal; 4=medium conchoidal; 5=good conchoidal