pseudomorph

American  

[soo-duh-mawrf] / ˈsu dəˌmɔrf /

noun

1. an irregular or unclassifiable form.

2. a mineral having the outward appearance of another mineral that it has replaced by chemical action.

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pseudomorph British  

/ ˈsjuːdəʊˌmɔːf /

noun

1. a mineral that has an uncharacteristic crystalline form as a result of assuming the shape of another mineral that it has replaced

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Other Word Forms

• pseudomorphic adjective
• pseudomorphism noun
• pseudomorphous adjective

Etymology

Origin of pseudomorph

First recorded in 1840–50; pseudo- + -morph

Explanation

A pseudomorph is kind of like a geological "imposter." It occurs when one mineral replaces another, taking on the outward shape and crystal form of the original mineral while being composed of a completely different substance. The word pseudomorph literally means "false form." In geology, a pseudomorph occurs when one mineral replaces another but keeps the original's shape. This process also happens with organic objects: Petrified wood, for example, is a pseudomorph. Over millions of years, silica replaces a dead tree's wood cells, resulting in something that looks like a tree — complete with bark textures — but is actually solid quartz. Outside of geology, the term can describe anything that maintains an old "shell" or appearance while its internal reality has completely changed.

Example Sentences

In this case, goethite is a pseudomorph after pyrite, meaning it has taken the form of another mineral.

From Textbooks • Jan. 1, 2017

It is a pseudomorph after iolite, and consists mainly of hydrous aluminium silicate.

From The New Gresham Encyclopedia Volume 4, Part 3: Estremoz to Felspar by Various

Cassiterite occurs as a pseudomorph after orthoclase felspar in some of the altered granite of Cornwall, and it has occasionally been found as a cementing material in certain brecciated lodes.

From Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 4 "Carnegie Andrew" to "Casus Belli" by Various