Pseudomorphs and variations
This Collection Arkane website section offers special mineral specimens of pseudomorphs and variations, especially from the Poudrette Quarry at Mont-Saint-Hilaire, Quebec Province, Canada (MSH).
A pseudomorph is a mineral species (or more) that retained the external crystal form of another mineral species but not its chemistry. A classic example is cubes of Goethite after Pyrite resulting from oxidation of the ferrous sulfide to ferric oxyhydroxide. A common example at MSH is Quartz and Siderite after Aegirine.
There are variations on the same theme called epimorph, paramorph and perimorph. An epimorph is a hollow cast (hole, cavity, space within) of a mineral species that has overgrown an intial mineral species that is now dissolved away. A common example at MSH is Analcime and Siderite crsytals after a larger Analcime crystal.
A paramorph is a pseudomorph with the same composition as the original crystal, caused by a phase transformation. A typical example is Calcite with Aragonite morphology. There seems to be no such known examples at MSH.
Finally, a perimorph is a mineral species crystal enclosing another mineral species crystal. This case is very common in nature especially with Quartz. There seems to be no such known examples at MSH.
There seems to be more than one hundred pseudomorphs and variations at MSH (pers. comm. of Gilles Haineault). Collection of such mineral specimens can be very fascinating.
Collectors who wish to investigate further the world of pseudomorphs and variations are invited to consult the mindat.org website and search for specialized publications about this matter. Definition of the pseudomorphs and other variations can also be found on Wikipedia website. Collectors especially interested in MSH pseudomorphs and other variations are invited to consult Gilles Haineault's book.
Text published: January 2017.