Pseudomorph

Pseudomorph

In geology, a pseudomorph is a mineral compound resulting from a substitution process in which the appearance and dimensions remain constant, but the mineral which makes up the chief component of the compound is replaced by another. The name literally means "false form".

Three kinds of pseudomorph exist:

An infiltration pseudomorph is a pseudomorph in which one mineral or other material is replaced by another. The original shape of the mineral remains unchanged, but color, hardness, and other properties change to those of the replacing mineral. An example of this process (also called substitution) is the replacement of wood by silica (quartz or opal) to form petrified wood in which the substitution may be so perfect as to retain the original cellular structure of the wood. An example of mineral-to-mineral substitution is replacement of aragonite twin crystals by native copper, as occurs at Corococo, Bolivia.

A variety of infiltration or substitution pseudomorphism is called alteration, in which only partial replacement occurs. This happens typically when a mineral of one composition changes by chemical reaction to another of similar composition, retaining the original crystalline shape. An example is a change from galena, lead sulfide, to anglesite, lead sulfate. The resulting pseudomorph may contain an unaltered core of galena surrounded by anglesite that has the cubic crystal shape of galena.

A paramorph (also called allomorph) is a mineral changed on the molecular level only. It has the same chemical composition, but with a different structure. The mineral looks identical to the original unaltered form. This occurs, as an example, in the aragonite to calcite change.

An incrustation pseudomorph results from a process by which a mineral is coated by another and the encased mineral dissolves. The encasing mineral remains intact, and retains the shape of the original mineral or material. Alternatively, another mineral may fill the space (the mold) previously occupied by some other mineral or material.

Pseudomorphs are also common in paleontology. Fossils are often formed by pseudomorphic replacement of the remains by mineral matter. Examples would include petrified wood and pyritized gastropod shells.

Terminology for pseudomorphs is "replacer "after" original", as in "brookite after rutile".

References

* "Dana's Manual of Mineralogy" by Cornelis S. Hurlbut, Eighteenth Edition, (1971, John Wiley & Sons, Inc.) ISBN 0-471-42225-8


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Look at other dictionaries:

  • Pseudomorph — Pseu do*morph, n. [See {Pseudomorphous}.] 1. An irregular or deceptive form. [1913 Webster] 2. (Crystallog.) A {pseudomorphous crystal}, such as a crystal consisting of quartz, but having the cubic form of fluor spar, the fluor crystal having… …   The Collaborative International Dictionary of English

  • pseudomorph — [so͞o′də môrf΄] n. [< Gr pseudomorphos, having a false form: see PSEUDO & MORPH] 1. a false or irregular form 2. a mineral possessing the external form characteristic of another pseudomorphism [soo΄dəmôr′fiz΄əm] n. pseudomorphous… …   English World dictionary

  • pseudomorph — pseudomorphic, pseudomorphous, adj. pseudomorphism, n. /sooh deuh mawrf /, n. 1. an irregular or unclassifiable form. 2. a mineral having the outward appearance of another mineral that it has replaced by chemical action. [1840 50; PSEUDO + MORPH] …   Universalium

  • pseudomorph — noun A mineral that formed by replacement of an existing mineral (or organic matter) such that the new mineral has the appearance and dimensions of the original. Petrified wood is a silicic pseudomorph of the original wood …   Wiktionary

  • pseudomorph Crystallography — [ s(j)u:də(ʊ)mɔ:f] noun a crystal consisting of one mineral but having the form of another. verb replace to form a pseudomorph. Derivatives pseudomorphic adjective pseudomorphism noun pseudomorphous adjective Origin …   English new terms dictionary

  • pseudomorph — noun Etymology: probably from French pseudomorphe, from pseud + morphe morph Date: 1849 1. a mineral having the characteristic outward form of another species 2. a deceptive or irregular form • pseudomorphic adjective • pseudomorphism noun •… …   New Collegiate Dictionary

  • pseudomorph — A mineral found crystallized in a form that is not proper to it but to some other mineral. [pseudo + G. morphe, form] …   Medical dictionary

  • pseudomorph — pseu|do|mọrph 〈Adj.〉 Pseudomorphose aufweisend, durch Pseudomorphose entstanden * * * pseu|do|mọrph <Adj.> (Mineral.): Pseudomorphose aufweisend …   Universal-Lexikon

  • pseudomorph — pseu|do|mọrph 〈Adj.; Min.〉 Pseudomorphose aufweisend, durch Pseudomorphose entstanden …   Lexikalische Deutsches Wörterbuch

  • pseudomorph — pseu|do|morph <zu ↑...morph> Pseudomorphose zeigend …   Das große Fremdwörterbuch

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