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Improving Mindat.orgMisuse of term "Pseudomorph"

16th Aug 2011 12:19 BSTJolyon Ralph Founder

As has been discussed in another thread here, we have quite a lot of photo contributors who do not understand the correct usage of 'pseudomorph' on

In order to be consistent, this is a simplified guide as to what is, or is not, a pseudomorph:

When one mineral, fossil or structure is replaced with a new mineral, it is in general called a REPLACEMENT.

When this replacement mimics the crystal form of the original mineral by taking over the space occupied by the previous crystal, the term pseudomorph is used.

If something is replacing a fossil, or a piece of wood, or a worm tube, or any other non-crystalline structure, then it is a REPLACEMENT, not a pseudomorph.

If something replaces a crystal of a previous mineral, then it is a pseudomorph. But, to be a pseudomorph the crystal form of the original mineral has to be visible in the new specimen. If the original mineral was an anhedral grain, then it's not a pseudomorph. If the new mineral has overgrown and replaced the original mineral to such an extent that no measurable or visible signs of the original crystal shape can be detected, then it's a replacement not a pseudomorph.

If something is the remains of a coating that was previously coating a now missing mineral, then it is an epimorph, not a pseudomorph.

if something has changed at the crystal structure level only, and there is no chemical change (for example, aragonite converting to calcite, but retaining the original shape of the aragonite crystal) then it is a paramorph - a special class of pseudomorph (so both terms are correct in this case, but paramorph is preferred).

If in doubt, use the term 'replacement' instead of 'pseudomorph'.



ps. This document is a work in progress. Please comment below if you think things could be explained better, or if you think anything is incorrect

16th Aug 2011 13:43 BSTEvan Johnson

"If the original mineral was an anhedral grain, then it's not a pseudomorph."

Maybe I'm reading too deeply into this, or maybe it's my lack of understanding, but this seems like it might not necessarily be true. If we are to assume that an anhedral grain can be a mineral (and I think that most would agree with that), and we partially (or completely, if demonstrable) replace it with another mineral, isn't it still a (not particularly attractive) pseudomorph? That is to say, we're replacing one lattice and composition with another- on an atomic scale, wouldn't euhedral and anhedral replacements appear similar? So, there is temporal but not spatial variance, with one accepted mineral species replacing another accepted mineral species. Actually, maybe that last sentence would summarise my view of pseudomorphism in general. Hope I'm not splitting hairs too far.



16th Aug 2011 13:56 BSTAntonio Borrelli Expert

To mud the waters I see sometimes the term "perimorph" used to describe particular type of pseudomorphs especially in older publiations.

From the following link I found a good description for the usage of this term: :

"5. Perimorph: Not to be confused with paramorph. A perimorph is a special type of pseudomorph which is formed when one mineral is encrusted by another, and then the original mineral is leached out leaving a hollow shell in the form of the original mineral. Epimorphs are a special case of a perimorph. L.P. Gratacap in his Popular Guide to Minerals (1912, 63) defines an epimorph as “a pseudomorph formed by encrustation as when quartz coats calcite, concealing the covered mineral completely though assuming the crystalline form of the calcite. Such phases of pseudomorphism are called epimorphs."

16th Aug 2011 14:44 BSTJolyon Ralph Founder


> isn't it still a (not particularly attractive) pseudomorph?

No, it's a replacement!

A pseudomorph HAS to be something that has a deceptive form taken after the crystallography of another mineral species.

If this form is not there, it's not a pseudomorph.

We tend to be forgetting that the word 'pseudomorph' means something very specific. A false (or deceptive) form. Out of laziness people have started using it for a mineral replacement of anything.

But not any more. Not on my website. We do things properly from now on :)


16th Aug 2011 14:45 BSTJolyon Ralph Founder

And is a perimorph and an epimorph the same thing? If not, what's the distinction?

16th Aug 2011 15:12 BSTAntonio Borrelli Expert

Nowadays probably the same thing.

But with my poor comprehension of the English language, in the description I pasted above I understand that in the past an epimorph of mineral X on mineral Y may not implied the leaching out of mineral Y. It was considered an overgrowth encrustation.

If you are thinking to edit a new page for 'pseudomorphs' or some sticky note at the top of some uploading form maybe this information should be added.

16th Aug 2011 15:39 BSTAlfredo Petrov Manager

On the other hand... Collectors use the word pseudomorph for siderite replacing calcite, and other such replacements where no change of shape, or false shape, was involved. Technically, pyrite after ammonite is more of a "pseudomorph" in the literal sense of the word than a siderite after calcite is. Traditional usage does not always correspond to logical usage or etymological origin.

We could simplify this issue by abandoning the word "pseudomorph" altogether and just lump all these phenomena together under the title "Replacements", which no one could quibble with.

16th Aug 2011 16:12 BSTJolyon Ralph Founder

Well, if siderite has replaced calcite to the extent that we can tell it was originally calcite - the definition of pseudomorph is perfectly valid. the form is false, doubly deceptive in this case because the form is one that calcite can take.


16th Aug 2011 16:38 BSTEvan Johnson


I really don't mean to be annoying or pedantic about it, but something still strikes me as intuitively wrong about when I drop or damage a malachite after azurite, breaking it (an experiment, with n=several that I have regrettably performed), it changes from a pseudomorph to a replacement- similarly with something damaged in a mining operation, or affected by weathering, or light. I fully understand "pseudo-" and "-morph," but to me it's like claiming something isn't crystalline simply by virtue of the fact that it does not show faces. That said, I of course accept your definition, and will let the issue go.



16th Aug 2011 17:07 BSTUwe Kolitsch Manager

The definition is clear when you have euhedral crystals, but less so when there are subhedral to poorly formed to globular crystals (and aggregates) on or in matrix - where to draw the line?

It would be interesting to compare the definition of pseudomorph etc. in several standard English and non-English mineralogy textbooks.

16th Aug 2011 18:22 BSTJolyon Ralph Founder

Evan - If you drop a malachite pseudomorph after azurite, and it breaks into a hundred pieces, and you pick up on of the chunks that is left and it has no discernable faces on it, is it still a pseudomorph? No - of course not! It's just malachite, that happened to have been formed as a replacement of azurite.

This is the clear distinction to me between a replacement (the malachite in this case is still a replacement of original azurite) and pseudomorph, which is a term to describe a visible relationship between the new mineral and the mineral it replaced.

As for where to draw the line - if measurable or visible signs of the original crystal shape can be detected then the term pseudomorph is approprite. If not, then it's just a replacement.

To say the chunk of malachite in the example above is still a pseudomorph is as nonsensical as describing a faceted gemstone as anhedral or euhedral based on the original crystal shape before it was cut.

Uwe - it may be interesting to note about other uses of the word 'pseudomorph' by collectors and in mineralogy books worldwide, but the key thing here is to come to a standard definition that will stick to internally.

16th Aug 2011 18:37 BSTEvan Johnson


Thanks for the explanation.


16th Aug 2011 19:04 BSTRick Dalrymple Expert

The Dictionary of Geologic Terms, 3rd Edition, Prepared by the American Geologic Institute gives the following definitions.

Replacement; 1. Metasomatism. 2. A process of fossilization involving substitution of inorganic matter for the original organic constituents of a plant or animal.

Pseudomorph; A mineral whose outward crystal form is that of another mineral; it is described as being “after” the mineral whose outward form it has, e.g. quartz after fluorite.

Metasomatism; The process of practically simultaneous capillary solution and deposition by which a new mineral may grow in the body of and old mineral or mineral aggregate. The presence of interstitial, chemically active pore liquids or gases contained within the rock body or introduced from external sources are essential for the process, which often, though not necessarily, occur at the constant volume with little disturbance of the textual or structural features.

I realize there are other definitions that may be used and printed in other publications. But I think these give a good basis for understanding what the differences are between these terms.

The definition for pseudomorph is limited to non-fossils and euhedral crystals. I think most of us do use the term “pseudomorph” loosely and we should use the term replacement instead. This would sound better than saying “quartz metasomatic fluorite”

The definition for metasomatism insinuates that a visible recognition of a crystal replacement is possible but I would think that a microscopic grain or crystal could be replaced without a visible identification.

And massive mineral aggregates that are replaced with a new mineral without euhedral crystals visible would be called a replacement and not a pseudomorph.

These definitions would support Jolyon’s guidelines.

Now for the term “altered”. From the same dictionary;

Alteration; Changes in the chemical or mineralogical composition of a rock, generally produced by weathering or hydrothermal solutions.

This definition seems to be the act changing of one mineral to another. The dictionary doesn’t list the words as nouns, verbs, etc. But it seems to me this is a verb where “replacement” is a finished product (a noun).

Using these definitions, an azurite crystal changing to malachite is actually altering as long as the geo-processes are still in action. Once the specimen is removed from the ground the geo-processes are done and it is then a pseudomorph (at least as pseudomorphed as it is going to get).

16th Aug 2011 19:42 BSTAthanasios Ziros

A quick and Greek linguistic approach to the subject:


Pseudo + morphosis derives from Greek Ψευδό + μόρφωσις

Pseudo means false in a deceptive way, fallacious

Morphosis means to take/give shape or pattern

Therefore concerning mineralogy the term is properly used when a mineral replaces another and you are initially tricked due to the crystal shape in wrong identification. The element of deceit is necessary.

No one is tricked with pyrite replacing an ammonite

You can however use from a grammatical point of view the term morphosis without pseudo to describe form i.e. Pyrite morphosis (morphene) after ammonite, meaning pyrite with the shape-form of an ammonite.

“Pseudomorphosis” has been widely used in theology, history and philosophy y since classical ages, mostly to describe heresy, controversial and false reciting of events, brainwashing, etc.


perimorph περι + μορφη means all around includeed by + form

epimorph επι+ μορφη means on top,above + form

paramorph παρα + μορφη means altered shape due to tension (in non elastic mateials like metals)

Best regards,


16th Aug 2011 22:27 BSTRock Currier Expert

All very interesting. We will eventually come up with a synthesis of what a pseudomorph is or isn't and the names, defitions and examples of each type, but I am waiting for Kieth Harshbarger to finish what he has started in terms of a description of each type, which I think will weigh heavily in my judgement of that we finally come up with and use in the Best Minerals pseudomorph article, because I think he knows more about pseudomorphs than anyone I know and has collected them all his life.

Currently I have cast a wide umbrella to cover as many pseudomorph type things as I can. I would eventually like to tag each locality entry type with the name of its pseudomorph type. There will never be complete agreement about what is absolutely correct here, and in those areas where there is reasoned logical dissent I would like to also present opposing points of view.

16th Aug 2011 22:54 BSTNorman King Expert

We seem to be missing something when it comes to crystallographic inversion. Jolyon mentioned it, but without using the term “inversion.”

Crystallographic inversion occurs where one mineral replaces another, but there is no change in chemical composition, such as aragonite inverting to calcite. As far as I know, this term is still used. So, I conclude that polymorphs can invert one to another, creating a paramorph, such as calcite after aragonite. I have also seen fairly recent accounts of the mechanism of opal-CT inversion to quartz. Opal-CT displays the x-ray characteristics of tridymite and low cristobalite, so this phase of the opal to quartz transformation apparently occurs after water is lost. The opal-A to opal-CT transformation is the stage when water is lost. I realize there is some uncertainty as to just what opal-A is, or what the range of things is that might have been called “opal” (opal-A), but restricting the discussion to the opal-CT to quartz transformation should take care of that. Previous authors I have read make just that restriction in application of the term inversion, but I am no expert, myself.

Nevertheless, the term “inversion” might also be mentioned here.

16th Aug 2011 23:18 BSTJolyon Ralph Founder

Rock said:

>those areas where there is reasoned logical dissent I would like to also present opposing points of view.

This is what this thread is for. But once we have decided on a use of the terms we really must make sure we stick to them throughout the site, otherwise it just becomes a mess.

But here, this debate is very welcome.

17th Aug 2011 08:38 BSTEmanuele Rambaudi

Personally I'd not disdain the use of the term "pseudomorph" for fossils, provided that the context should be kept in mind: in labelling a pyritized ammonite, I would write, for instance, "Bifericeras bifer" and then add, as a sidenote, that it's composed of pyrite; in a "mineralogical" context, i.e. if for some reason the specimen should be included in a mineralogical collection / database and the stress is on the mineral, I'd feel free to write "pyrite pseudomorph after Bifericeras bifer" (as far as the web is concerned, both wikipedia and the Britannica report this use of the word). Of course, since I'm speaking about a fossil with a given name, I would be more satisfied with the first definition.

A "looser" use of the word "pseudomorph" can also be seen in natural sciences, when speaking about those ink clouds that many cephalopods use to deceive predators, aiming to mimick the size and shape of the squid itself.

That said, if the term "replacement" may be more handy for classification issues here in Mindat, that's ok for me. :)-D

Last notes. As Antonio was saying some posts before: an epimorph occurs when a complete coating takes place; a perimorph occurs when a coating takes place and the coated mineral is no longer present (what you see is only a hollow shape). The use of these terms is neither so widespread nor of simple understanding, but they might be considered pseudomorph sub-categories and sometimes come in handy. P.S. The name of the author "Gratacap" quoted by Antonio resembles the italian "grattacapo", which means more or less "nuisance, trouble, headache". A coincidence? :)



17th Aug 2011 13:43 BSTRalph Bottrill Manager

Jolyon's definition is fine but it's interesting to note the original definition:

The term pseudomorph (French = la pseudomorphose) was coined by René Just Haüy (1743-1822) in his epochal Traité de Mineralogie  (1801, Vol. 1, 140).  Haüy did not, however, use it in its present sense. As part of a general discussion about types of concretions he coined the term from the Greek pseudo (false) and morph (form) for mineral bodies that owed their outward form to circumstances other than their own unique powers of crystallization or formation.  Most of the discussion was devoted to fossils, especially fossil shells and petrified wood.  He also included at the end of the discussion, the comment “...bodies which have a false and deceitful figure” which “...present in a very remarkable manner foreign or strange forms which they have in some measure obtained from other bodies which had received them from nature (ibid.).”  After considerable discussion of what we would now classify as fossils, he adds that, “The mineral kingdom also has its pseudomorphoses. We find some substances of this kingdom under crystalline forms which are only borrowed; and it is probable that, in some cases at least, the new substance has been substituted gradually for that which has ceded its place to it as we suppose takes place with respect to petrified wood (ibid.).”


Personally i feel it safer to use "replacement" or "overgrowth" unless the original crystal form is very clear. Too many "pseudomorphs" need a lot of imagination to see the original crystals, eg. and many are better termed overgrowths, but the term obsesses many collectors.

Metasomatism is used more for rocks than minerals.

17th Aug 2011 13:55 BSTJolyon Ralph Founder

We really have to make sure our usage agrees with current scientific usage.

If you are a professional mineralogist, petrologist or palentologist, I'd be very interested to hear what you believe is the correct scientific usage of the term.

Also, if the term has been defined in any style or editorial guides for mineralogical or other earth sciences publications, again we should listen to what they say.

It's current scientific usage that is important, historical roots and usage, and what normal collectors use the term for are interesting, but a diversion.


17th Aug 2011 14:37 BSTEarl Verbeek Expert

Sorry to muddy the waters here, but what about the following?

1. "Infiltration pseudomorphs"- If crystals of one mineral (e.g., halite) encased in sediment or rock dissolve, and another mineral subsequently precipitates in the crystal-shaped voids, you have (to my mind at least) a valid pseudomorph. However, the later mineral simply filed a void -- it did not replace an earlier one.

2. Hydration-dehydration pseudomorphs- Tincalconite after borax is one example. I do not think of dehydration as a replacement process, but perhaps others do. And what about autunite from the Daybreak mine, which can be autunite one day but meta-autunite another, depending on relative humidity? Here there is no discernible change in external appearance at all.

3. "Radiation pseudomorphs"- If the lattice structure of a zircon crystal is destroyed by radioactive decay of thorium as an impurity element, thereby resulting in an amorphous (metamict) zirconium silicate "glass," is this not a special type of pseudomorph?

17th Aug 2011 17:33 BSTPeter Haas Expert

There are no contradictions to what Jolyon was trying to say. Simply speaking, the term "pseudomorph" refers to a state, which can be obtained in different ways. Usage of the term does not imply any particular formation mechanism.

17th Aug 2011 18:29 BSTRoger Lang Manager

I refer to this article when using the term pseudomorph:

Strunz, Hugo (1982): Pseudomorphosen - Der derzeitige Kenntnisstand. Versuch einer Klassifizierung. - Der Aufschluss, 33, pp 313-342.

It´s in german .. but maybe somebody has the time to translate ;-) .. i haven´t at the moment ...



18th Aug 2011 12:45 BSTEarl Verbeek Expert

Peter- my point exactly, that whatever definition of pseudomorph Mindat eventually utilizes, it should be nongenetic (i.e., not implying any particular process(es)). That's why I posted those three examples, all of which I thought adhered to the general concept of "pseudomorph." I look forward to further comment -- quite an interesting discussion going on here.

18th Aug 2011 13:57 BSTRalph Bottrill Manager

Interesting too, that wikipedia's definition of pseudomorphs specifically mention petrified wood! I quite agree that definitions change and the present definition is probably the most generally used, but I suspect it depends what Uni you went to.

(You can see why the collective noun for geologists is an "argument")!

18th Aug 2011 14:12 BSTJolyon Ralph Founder

well, that's easy to fix :)

18th Aug 2011 16:42 BSTChester S. Lemanski, Jr. Manager

Petrified wood is a fossil! It may be listed as a variety of cryptocrystalline quartz, opal, pyrite, calcite, carnotite, or whatever other mineral species may be the replacement material, but it is a fossil nonetheless. The replaced material was not a mineral to begin with so it also doesn't fit the definition of mineral Y after mineral X. Finally, the form which is retained is not crystallographic in nature.

18th Aug 2011 16:43 BSTWilliam C. van Laer Expert

Several different textbooks on mineralogy define pseudomorph a little least one defines it also as an "encrustation" pseudomorph, while other texts do not mention this mechanism at all. This brings to mind one famous example that I have always had a problem with...and repeatedly to be found in the Mineralogical Record, Vol. 24, No. 3 (may-June 1993); page 195, Figure 13, which shows a microcline crystal encrusted with random topaz and quartz crystals...not even remotely resembling the original form of the microcline crystal...perhaps more technically a "replacement", but another example of the editor's failure to properly edit his publication, and the author's (Michael A. Menzies) fertile imagination.

18th Aug 2011 19:41 BSTJohan Kjellman Expert

I see a lot in the following reference pertinent to this discussion but don't have the time to translate or extract.

For you who read german - enjoy. For you who don't - maybe an evening class will make for a new richer life!!


18th Aug 2011 21:42 BSTJim Robison

I'm traveling and don't have access to my library right now. This whole topic never fails to generate lots of opinions and definitions, almost all of which have some merit.

If I had access to my papers, I would turn to an article in Rocks and Minerals several years back when John Sampson White, I think, had several pages on the definition of a pseudomorph, etc. in an excellent article. (Perhaps someone on the forum can cite the article).

In addition, there is a real expert on this topic in California (actually a husband and wife pair). Si and Ann Frazier have spent many hours over the past decades studying, and writing about, pseudomorphs, starting with the Gratacap paper, and references well before that, and up to recent years. If I can, when I return, I'll scan Si's presentation to one of the California mineral society meetings and add it as a pdf file, after I get permission from the Frazier's to do that.


19th Aug 2011 05:31 BSTRock Currier Expert

Here is the text about pseudomorphs that Kieth Harshbarger has written so far for the best Minerals pseudomorph articles. Im sure he will appreciate your comments on it.

Evolution of a Pseudomorph

The term “Pseudomorphoses” was coined by the French crystallographer, the Abbe Rene Just Hauy in 1801(Traite de Mineralogie, Vol 1, pp140-5) . In his study, he believed the pseudomorph to be a type of concreation, which displayed a ‘’False or Deceitful’’ form. They were to be created thru the infilling of a foreign material in the viod , once occupied by another object – MOLDS & CASTS. Most of his examples, dealt with preserving the shape of shells and woods. To him, a pseudomorph was more likely to represent a mineralized fossil, a concept often ignored today. He did state, however that similar things did occur in the Mineral Kingdom.

A MOLD represents the hollow impression, resulting from the removal of the original host from a more resistant matrix. The interior wall-zone now preserves the overall shape of the original material. From those impressions, the identity of the host may be identified. They have been called Solution Pseudomorphs or Negative Crystals.

Ex Quartz Mold after Glauberite, Upper New Street Quarry, NJ

Quartz Mold after Fluorite, Cumberland, England

A CAST results from the simple infilling of any new material in the hollow MOLD. This thus can create a replica after the original host. Now it helps if the CAST is of a more resistant material than the enclosing matrix, so they may weather out for study. Called by some; Infiltration Pseudomorphs.

Ex Quartz Cast after Glauberite, , Lower New Street Quarry, NJ

Opal Cast after Shell, Australia

Quartz Cast after Halite, Arizona

Another slightly different hybrid case, involves two different, free-formed minerals, growing side by side. As they increase in size, they may create a common Interface. With the removal of one of the pair, an impression of the vanished species may remain on the side of the remaining crystal. The Swiss call this partial MOLD, a “Narben”, meaning Scar.(Frazier 2005 MSSC).

19th Aug 2011 11:26 BSTJohan Kjellman Expert

I see that the link I provided starts on the title page. I was hoping it should be directed directly to the "Einleitung" pp 1-11.

Blum goes through the history of the pseudomorph concept, starting with Werner, Breithaupt, Haüy, Hausmann, Naumann, Haidinger and Landgrebe. Then he goes on discussing different types.


19th Aug 2011 12:59 BSTJolyon Ralph Founder

Thank you Rock.

No-one doubts that when Hauy used the term 'pseudomorph' he was considering fossils as well as minerals, but then terms change over time. We no longer refer to red spinel as 'Ruby', but that was allowed with the original definition.

The debate has been going on for some time. By the 1860s we already had the same arguments as we're having here!

Mr James Plant read a paper "On the so called Pseudomorphous Crystals of Chloride of Sodium found in the Upper Triassic rocks of Leicestershire and the adjoining counties".

Mr Plant gave Bischof's definition of the term pseudomorphous stating that it is applied to such minerals as possess geometrical forms foreign to themselves and acquired in a way entirely different from crystallization They are divided into two classes first alterative pseudo morphs produced either by removal addition or exchange of constituents; second displacement pseudomorphs produced by incrustation or by replacement. But the pseudomorphs found in the Triassic rocks belong to neither of these classes they are produced by a deposition of substances in cavities left in rocks by the solution of imbedded crystals analogous to casting in a mould, thus though the outside of the cast assumes all the minute appearance of a crystal the inside possesses none of the properties of a true crystal having no cleavage planes axes etc.

19th Aug 2011 21:52 BSTRock Currier Expert


Yes, you are right. Kieth is not trying to revert us to Hauy's old definition, but to give us a sense feeling where the term pseudomorph came from and its original usage.

12th Oct 2016 15:47 BSTAlfred L. Ostrander

Hello All,

I am just kicking this thread up to the top of the heap, so to speak. Under the General category a thread has been running on pseudomorphs. Lots of great photos of minerals and a lot of things that may or may not be pseudomorphs. Maybe this discussion should continue to support the clarification of definitions Jolyon wants for usage on Mindat.

Best Regards,

Al O

12th Oct 2016 18:32 BSTSteve Hardinger Expert

Maybe there should be a separate Messageboard category for pseudomorphs. The format would be modeled after other threads, but have a different composition.

12th Oct 2016 20:30 BSTRolf Luetcke Expert


Your point is well taken and it was very nice to read the older thread Jolyon posted.

I have myself used the term "loosely" since it is a forum to show off "replacements" and I agree, I need to be more careful with the term.

I was hoping it was a place for people to share favorites and to a great extent it has been just as I had hoped.

As with mineral species and locations, one needs to be as accurate as possible and I have to say, I have learned a thing or two on the thread myself.

I appreciate peoples interest in what I think is a wonderful sub category of mineral collecting.


12th Oct 2016 22:51 BSTAlfred L. Ostrander


The pictures have been great! Some just might not be pseudomorphs. That poses a question that is difficult to answer as the usage through time seems to have been clouded up a bit and much doesn't appear to be what the Abbe Rene Just Huay intended. Some the applications of the term through have been replaced by better terms with clearer definitions. I'm still sorting out some of those terms myself and don't mind asking for insight on clearer definitions. I did some great time at university studying things geologic. I have had a lot of years at this mineralogy thing and still want to keep on learning. I've got my index cards laid out for terms such as perimorph and paramorph, etc. and am getting the best definitions for each term that I can find. Maybe not what Sherlock intended but the game is afoot!

Best Regards,

Al O
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