Conchoidal fracture

Conchoidal fracture
Obsidian gives conchoidal fractures

Conchoidal fracture describes the way that brittle materials break when they do not follow any natural planes of separation. Materials that break in this way include flint and other fine-grained minerals, as well as most amorphous solids, such as obsidian and other types of glass.

Conchoidal fractures can also occur in other materials under favorable circumstances. This material property was widely used in the Stone Age to make sharp tools, and minerals that fractured in this fashion were widely traded as a desirable raw material.

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 (Greek konche[1]). A swelling appears at the point of impact called the bulb of percussion. Shock waves emanating outwards from this point leave their mark on the stone as ripples. Other conchoidal features include small fissures emanating from the bulb of percussion.

They are defined in contrast to the faceted fractures often seen in single crystals such as semiconductor wafers and gemstones, and the high-energy ductile fracture surfaces desirable in most structural applications. See the main article on Fracture.

Lithics

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. As conchoidal fractures can be produced only by mechanical impact, rather than frost cracking for example, they can be a useful method of differentiating prehistoric stone tools from natural stones.

Conchoidal fracture in art

Conchoidal fracture in glass

Conchoidal fracture as originally developed by prehistoric people is used by highly skilled artists to craft bifacial glass pieces for ornamental, as well as functional sculptures.[citation needed]


References

  1. ^ "conchoidal". Merriam-Webster Online. http://www.merriam-webster.com/netdict/conchoidal. Retrieved 2010-10-30. 

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См. также в других словарях:

  • conchoidal fracture — kriauklėtasis lūžis statusas T sritis chemija apibrėžtis Kiaukutus primenantis lūžio paviršius. atitikmenys: angl. conchoidal fracture rus. раковистый излом …   Chemijos terminų aiškinamasis žodynas

  • Fracture — Frac ture (?; 135), n. [L. fractura, fr. frangere, fractum, to break: cf. F. fracture. See {Fraction}.] 1. The act of breaking or snapping asunder; rupture; breach. [1913 Webster] 2. (Surg.) The breaking of a bone. [1913 Webster] 3. (Min.) The… …   The Collaborative International Dictionary of English

  • fracture — [frak′chər] n. [ME < OFr < L fractura, a breaking, breach, cleft < pp. of frangere, BREAK] 1. a breaking or being broken 2. a break, crack, or split 3. a break in a body part, esp. in a bone, or a tear in a cartilage: see COMPOUND… …   English World dictionary

  • Fracture (mineralogy) — This article is about the terminology used to describe fracture surfaces. For fractures in rocks and minerals per se, see Fracture (geology) In the field of mineralogy, fracture is a term used to describe the shape and texture of the surface… …   Wikipedia

  • Fracture — For other uses, see Fracture (disambiguation). v · d · e Materials failure modes …   Wikipedia

  • 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. [1913 Webster] …   The Collaborative International Dictionary of English

  • fracture — fracturable, adj. fractural, adj. fracturer, n. /frak cheuhr/, n., v., fractured, fracturing. n. 1. the breaking of a bone, cartilage, or the like, or the resulting condition. Cf. comminuted fracture, complete fracture, compound fracture,… …   Universalium

  • conchoidal — conchoidally, adv. /kong koyd l/, adj. Mineral. noting a shell like fracture form produced on certain minerals by a blow. [1660 70; CONCHOID + AL1] * * * …   Universalium

  • conchoidal — adjective a) Describing a type of irregular fracture that occurs in materials with no natural plane of separation, such as flint. b) having smooth shell shaped convex and concave surfaces …   Wiktionary

  • conchoidal — [kɒŋ kɔɪd(ə)l] adjective chiefly Mineralogy denoting a type of fracture in a solid which results in a smooth rounded surface resembling a scallop shell …   English new terms dictionary


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