FMF - Friends of Minerals Forum, discussion and message board

[John S. White]

Was thinking that it might be interesting to start a thread showing photos of epitaxy. A very simple definition is the condition where one mineral is attached to another in a relationship that is controlled by the mutual crystal structures.

My first contribution to this thread is a photograph of spessartine and apatite in which the 3-fold axis of the spessartine is parallel to the 6--fold axis of the apatite.

[parfaitelumiere]

Good idea!
Here are some twins of arsenopyrite on pyrite!
Many years ago I had a good cumengite on boleite, with paratacamite...

[parfaitelumiere]

Here is a picture to show how it grows through the pyrite crystal.
The arsenopyrite does the same on other axes, but I can't draw it, because I have not the specimen in the hand!

[Jordi Fabre]

This is my contribution to this fascinating topic.

(More info about the Rutile-Ilmenite-Hematite from Zambia here: https://www.mineral-forum.com/message-board/viewtopic.php?t=155 )
(More info about the Rutile-Hematite from Brazil here: https://www.fabreminerals.com/specimens/RSBR-brazil-notable-specimens.php#EJ26F4 )

[Jojm]

Hi all,
This is my first contribution to this English forum.
As English is not my native language, please be lenient towards my future mistakes or misspellings.
I'm living in th west of France, not far from Nantes. I'm a microminerals collector and photographer.
Uranium minerals and more widely phosphates are my favorite subjects.
Very interesting thread, following Jordi message about rutile and hematite, a sample from Saint-Chistophe-en-Oisans and a second one from Boucheron mine.
Jean-Marc.

[Jordi Fabre]

Wonderful images Jean-Marc, thank you for sharing them with us!

Jean-Marc Johannet is a well-known French photographer. His work is frequently published in French magazines (and others), we are lucky to have him here publishing their photos.

Jordi

[parfaitelumiere]

really interesting thing here!

[Gail]

Jean-Marc, Thank you for the incredible photographs! I have been in Nantes a few times and love the area where you live. Please continue to share your amazing photographs?
All the best!

[Michael Shaw]

This specimen consists of marcasite epitaxial on pyrite from the Rensselaer Quarry, in Jasper County, Indiana.

[Jojm]

Gail, Jordi,
Thank you for your kind comments.
A less described epitaxy growth, smithsonite on dolomite.

[Tracy]

These photos are amazing!

- Tracy

[Joseph Taggart]

This is my contribution of photographs of a specimen demonstrating epitaxy.

The specimen shown is two crystals of sphalerite with an epitaxially controlled coating of chalcopyrite crystals from Joplin, Missouri. One photo shows the "front" of the specimen, showing the parallel orientation of the chalcopyrite crystals- by the light reflecting simultaneously off all the chalcopyrite crystals growing on the larger sphalerite crystal on the right. The other photograph is the "back" of the specimen showing the enclosed sphalerite crystals (largest crystal again located on the right) .
Size of specimen is 2 1/4" x 1 3/4" x 1 1/4". I purchased the specimen in Joplin, Missouri, in August of 1971.

[vic rzonca]

Does epitaxy relate to different minerals growing together and/or the same mineral that changes habit or orientation in the same specimen?

[John S. White]

Vic, I think you will find that the classic definitiion of epitaxy requires that the two crystals be different species. Habit changes with just one mineral during growth are quite common and if these were to be included it certainly would dilute the meaning of epitaxy. For my purposes I shall limit the definition to one mineral being non-randomly attached to another mineral. I hope everyone agrees.

[Pete Richards]

While I think John White's working definition of epitaxy as requiring two phases is useful for guiding this thread, I disagree, John, with your restriction from the larger context of studying epitaxy. I have argued in the past, and continue to believe, that the term can appropriately be extended to include the overgrowth of one mineral on itself. However, this is only useful if the texture of the assemblage provides strong evidence that there were two distinct stages of growth (as opposed to merely a change in the habit). Examples include multiple cube-octahedral galena crystals attached to a first generation galena with cube habit, calcite growing in very distorted shapes from spots along the edges of first-generation crystals, and calcite growing in twinned orientation as many tiny parallel "teeth" on a first generation crystal. I suppose the Mariposa calcites from Mexico, part of another recent thread, would also be an example.