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Improving Mindat.orgThe term "after"

4th Aug 2010 18:32 BSTReiner Mielke Expert

http://www.mindat.org/photo-324838.html Describing this specimen as malachite "after" chalcopyrite isn't strictly correct (other than time wise). "After" implies a "pseudomorphic" relationship. The proper terminology in this case would be malachite on chalcopyrite or coating chalcopyrite.

4th Aug 2010 19:17 BSTRob Woodside Manager

Right you are Reiner. There's a host of "-morph" habits and they are seldom correctly used. If the malachite replaced the chalco entirely while maintaining the shape of the chalco then we'd have a pseudomorph. I don't know if there is a name for a partial pseudomorph or at which point a "coating" becomes a pseudomorph. However a "coating" is an addition of material and not a replacement which is essential to pseudomorphoses. From Quiruvilca there are wonderful tennantites in epitaxi on enargites. There are killer iridescent xl specimens that sadly tarnish. Both minerals are black and sometimes the tennantite completely encloses the enargite. They are sold as pseudos but I never saw a replacement of the enargite with tennantite. Another common error is to call a cast a pseudomorph. Here a xl forms and other material overgrows it outlining the shape of the first xl. Then the first xl dissolves away leaving the second mineral with the shape of the first. This is called an epimorph (Edit: Epimorph when the first xl still exists, Perimorph when dissolved away)) and there is no replacement as required by pseudomorphoses. Since Dana III epimorphs and perimorphs considered as pseudos!!! See link belowA good example are the famous yellow Tristate Hemimorphites that are epimorphs of calcite.


Perhaps others could educate me on any other "-morphs"?

4th Aug 2010 19:53 BSTReiner Mielke Expert

I have often wondered about this. As you suggested the term has been misused. Seems to me that strictly speaking a pseudomorph must involve a complete replacement of the original mineral, otherwise the correct term should be for example: malachite partly replacing cuprite. Of course who is going to break open a crystal to find out if it is a complete replacement? Then of course there are the paramorphs.

4th Aug 2010 20:04 BSTRob Woodside Manager

Sometime damage can be very educational. The Onganja cuprites were coated with malachite. Only when broken do you see the wonderful cuprite. An unbroken one leaves you guessing!!! Thankfully there are lots of damaged ones.

5th Aug 2010 12:11 BSTRock Currier Expert

The Onganga malachites altering to cuprite have, in most cases only a thin skin of malachite and on some few specimens this has been removed with hydrochloric acid to show the still almost entirely intact cuprite crystal.


Pseudomorph is not a well defined term and is used by many different people to mean many different things from drusy quartz growing over whatever to casts after whatever to true complete chemical replacement or alteration of the structure of the mineral. We may be better off to leave it alone rather than to try and refine the definitions. The IMA has made many changes during the last few years that those alone are difficult to live with. I don't know how much more I can stand.

5th Aug 2010 17:24 BSTReiner Mielke Expert

Hello Rock,


As far as I can tell you can stand a lot!:)-D

5th Aug 2010 19:55 BSTBarb Matz

I'm so glad to see this discussion. My education and understanding is that a pseudomorph is a complete replacement that retains the morphology of the original. I have been *corrected* about my labeling a few times but that won't change my mind.

5th Aug 2010 19:57 BSTWilliam C. van Laer Expert

Some collectors call encrustations of one mineral over another "pseudomorphs", even though the secondary encrustation doesn't even resemble the crystal being covered...there are varying degrees of this, from those encrustations that DO resemble the mineral being covered, to those where the random orientation of the encrusting mineral grows in almost every possible direction, but not remotely appearing like the earlier mineral. Some textbooks call this an "encrustation pseudomorph", but where to draw the line? Since the encrusting mineral is not actually replacing the mineral underneath, I think the term encrustation psuedomorph should be considered a misnomer. A good example of this are the microcline crystals found by Menzies in the Sawtooth Batholith that are partly encrusted with acicular topaz crystals, but not following the form of the microcline crystal underneath.

5th Aug 2010 20:58 BSTDavid Bernstein Expert

I'm glad Reiner brought this up since the photo when posted, caused confusion in my mind. I recently collected material similar to this from another Ct. location and it never occurred to me to label it *Malachite after Chalcopyrite*(with Baryte), sexy as it might sound.

5th Aug 2010 21:30 BSTSteve Hardinger Expert

I've suggested this before, and I'll suggest it again: A Mindat mineralogical terms glossary would be useful in cases like this. I have one for organic chemistry terms (the Illustrated Glossary of Organic Chemistry). Students in my class (and around the world) make copious use of it.

5th Aug 2010 22:03 BSTMichel Gadoury

Hello,

Here's a good text about the many definitions of the term "pseudomorph" by Si Frazier.

Thanks to Denise Bicknell who provided me the link.

http://www.mineralsocal.org/bulletin/2005/2005_jan.htm

5th Aug 2010 22:28 BSTRob Woodside Manager

Thank you so much for a great link!!! I stand corrected on epimorphs. When an incrustation has the form of the still existing underlying xl it is an epimorph and when the underlying xl has been dissolved away it is a perimorph. Good to see that teeth, bones and fossils are still pseudos!!!


"Same shape" seems like the basic idea for pseudos rather than replacement.::o

5th Aug 2010 23:49 BSTJim Robison

Rocks and Minerals had an excellent article on this topic several years ago (I think by Robert Cook) My copy is in Arizona, and I'm in Washington for a spell so can't access it, but someone who can might take a look-see. I don't recall the distinction of perimorph and epimorph, but its been a while since I read the article.

6th Aug 2010 10:41 BSTRock Currier Expert

A source of definitions that I have found particularly useful is


A dictionary of mining, mineral and related terms published by the US Department of the Interior, Bureau of Mines.


I believe the contents of this volume since it was paid for by the US taxpayers is public domain information and I have often thought that it might be useful to incorporate it into Mindat and accessed through a third query field at the bottom of mindat pages along with species and locality. A huge amount of work if one were to manually enter it.


Google provides definitions of pseudomorph, perimorph and possibly epimorph if one wanted to go digging through pages of drug related stuff.

6th Aug 2010 11:41 BSTDavid Von Bargen Manager

If the glossary is the one I'm thinking about, although it was published by the Bureau of Mines, the copyright is held by the AGI.

8th Aug 2010 07:33 BSTKeith Compton Manager

Thanks Michel - I hadn't seen that particular article before. Very good.


Cheers

8th Aug 2010 10:07 BSTMark Willoughby Expert

Howdy All,


I like the idea of a 'Basic Geological and Mineralogical Glossary' on here so much, I am putting one together, it will take a couple of days by the time it is finished and added as an article.

I have gone through a few messages to find a few terms that have caused issues in the past, including this one, so, any terms or words you think should be included let me know.

Just remember though, I'm keeping it fairly 'basic' at this stage, so no really obscure technical terms that are relative only to specialty fields, we can expand it more later.



If you would like to see what I have already put on the list you can view it here


http://www.mindat.org/article.php/986/0/32296


the article will not go 'live' until the meanings for what is already there are finished.

8th Aug 2010 18:22 BSTJohn M Stolz Expert

Hey guys--great discussion and one that I certainly appreciate.


Michel, that citation is very informative--thanks. (Although I do wish it didn't bash the Germans so much--I like the language!) And like Rob, I conclude that as the prefix/suffix suggests, we're generally talking about a misleading or false appearance--so I guess I really don't get why encrustations would be considered a subset at all.


Even now as I'm typing, it occurs to me that residual soils could be construed to be a type of pseudomorph due to solution weathering.


Mark--good on you for starting this important project.

9th Aug 2010 00:17 BSTRock Currier Expert

Mark,

Thats a good effort. It would be better and more authoritative if you would list the sources of your definitions. Are you familiar with the dictionary of mining, mineral and related terms published by the US Bureau of mines? At its end it lists 10 pages of references that have been used on the creation of this dictionary and a page of abbreviations as well. Sometimes they have a number of definitions for the same work, each siting a different source and those sources are often defining the word as it is used in a different field. It might be useful if you could contact the Bureau of Mines or the Department of the interior and see if they would give us permission to use this huge existing list of definitions here on line on mindat. Perhaps they may already have it in a digital searchable format that could be incorporated here as a searchable entity.

9th Aug 2010 03:01 BSTMark Willoughby Expert

Howdy Rock,


I was fully intending to list my references at the end, as well as add notes regarding people posting other words and phrases they would like to see added.

At this stage you can only view it via the link in this thread.

9th Aug 2010 12:23 BSTRock Currier Expert

OK, go for it. It will help.
 
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