In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form ( crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another. The name literally means "false form". Terminology for pseudomorphs is "''replacer'' after ''original''", as in ''brookite'' after ''rutile''.

Substitution pseudomorph

Native copper pseudomorph after aragonite, western Bolivia

An infiltration pseudomorph, or substitution 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 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 Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pr ...

twin crystals by

native copper Native copper is an uncombined form of copper that occurs as a natural mineral. Copper is one of the few metallic elements to occur in native form, although it most commonly occurs in oxidized states and mixed with other elements. Native copp ...

, as occurs at the

Corocoro United Copper Mines The Corocoro United Copper Mines, Ltd. was the largest copper mine in Bolivia, an honor previously held by Compania Corocoro de Bolivia. The corporate office was at 151 Finsbury Pavement House, London, England, while the mine office was at Coro ...

of Coro Coro,

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

. 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 Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It cryst ...

(lead sulfide) to

anglesite Anglesite is a lead sulfate mineral with the chemical formula PbSO4. It occurs as an oxidation product of primary lead sulfide ore, galena. Anglesite occurs as prismatic orthorhombic crystals and earthy masses, and is isomorphous with barite and ...

(lead sulfate). The resulting pseudomorph may contain an unaltered core of galena surrounded by anglesite that has the cubic crystal shape of galena.

Paramorph

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

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...

change.

Epimorph and incrustation pseudomorph

An incrustation pseudomorph, also called epimorph, 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.

In other fields

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

biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary ...

, a pseudomorph is a cloud of mucus-rich ink released by many species of

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, a ...

. The name refers to the similarity in appearance between the cephalopod that released it and the cloud itself, in this context meaning literally "false body". This behaviour often allows the cephalopod to escape from predation unharmed, and is often performed as part of what is known as the blanch-ink-jet maneuver. In philosophy, the concept of pseudomorphosis was used by the German philosopher Oswald Spengler to describe how the forms of an older, more widely dispersed culture condition the expression forms of a younger, emerging culture, leading the latter to develop into forms that are fundamentally alien to its own world-feeling, and thereby preventing it from fully developing its own self-consciousness. In

archaeology Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscape ...

, organic pseudomorphs are impressions of organic material that can accumulate on the surface of metal artifacts as they corrode. They may occur when metal artifacts are buried in contact with organics under damp soil.0. de Alarcon, "Of Daggers and Scabbards: Evidence of Organic Pseudomorphs and X-Radiography." Penn Museum Blog. 16 April 2016. https://www.penn.museum/blog/collection/conservation/of-daggers-and-scabbards-evidence-from-organic-pseudomorphs-and-x-radiography

References

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

Substitution pseudomorph

Paramorph

Epimorph and incrustation pseudomorph

In other fields

See also

References