FMF - Friends of Minerals Forum, discussion and message board

[nurbo]

If you have two minerals formed one immediately on top of the other in a floater formation, both of which are in the same crystal system Is this Epitaxy? Further supposing that one crystal was on a matrix, could the other be said to be epitaxial on the first?

[Matt_Zukowski]

Epitaxy is not just one mineral growing on another. It is the oriented growth of one mineral on another. The crystal structure of the overgrowing mineral lines up in some way with the crystal structure of the original mineral. Yes you can have a mineral in the same crystal class growing epitaxily on another, but again, the second mineral must align with the first for it to be considered epitaxy.

[nurbo]

Thanks Matt,
Thats interesting, I ask because I found a cube which starts out as Fluorite and ends up as Galena without seeming to change dimension, it looks like the Galena finished off the cube started by the Fluorite.

[Riccardo Modanesi]

hi to everybody!
And what can you tell me about the fluorite+pyrite association, many specimens of it coming from China? (and hopefully not MADE IN CHINA! Hahahaha!!!)? is it epitaxy as well?
Greetings from Italy by Riccardo.

[Jordi Fabre]

[Tracy]

I'd like to see a photo of the fluorite-becoming-galena cube too...

- Tracy

[nurbo]

Hi all,
Its a favourite piece of mine now because of the variety of minerals present, some of the Galena has corroded into Cerussite and there are some Siderite crystals around the outside of the cube, Im not 100% sure this is an epitaxial relationship it just got me thinking about how epiitaxy works among minerals of the same crystal system, It could be that by some freak occurance the Galena ended up deposited on the end of the Fluorite, but if so the sizes of the two are wierdly similar,. There was no Galena outside of the matrix present on any of the pieces that came from the lump I trimmed this off nor did I find any Cerussite outside of this small area.. I love these lind of mysterious pieces
Ill do some photo's let you decide

Ricardo I know nothing of Chinese minerals Im afraid, I dont collect them beyond the odd lump of eye candy that I get for a real bargain.

[Pete Richards]

I'll be interested to see some photos too!

To my knowledge, epitaxy between galena and fluorite has not been well demonstrated, though Lance Kearns reported fluorite possibly epitactic on galena in a 1978 Mineralogical Record article. There's about a 9% misfit between the spacings in the two lattices, rather high for epitaxy, but not unheard of. Also, epitaxy between sulfides and non-sulfides is relatively uncommon.

[Riccardo Modanesi]

Hi Jordi!
I don't have a photo unfortunately, and I didn't even on buying it because I thought it was an artifact. I saw it many a time, expecially in Idar-Oberstein. It is green-purple fluorite surmounted by pyrite and it appeared polished as well, expecially in form of "slices".
Greetings from Italy by Riccardo.

[nurbo]

Hello I added the photos I did of this piece to my collection thread, the link is https://www.mineral-forum.com/message-board/viewtopic.php?p=24155#24155 It was hard to photograph because its so small, approx 4 mm on edge

p.s. Hi Riccardo, if I wasnt confused before I surely am now?

[Jordi Fabre]