FMF - Friends of Minerals Forum, discussion and message board

[Paul S]

Because I'm trying to find mineral specimen that go with my synthetic ones, I am of course also looking for mineral forms of bismuth. I have some nice specimen in my collection (nuggets, crystal masses, small single crystals), but I am still looking for something I don't even know excists!

Synthetic bismut crystals will form a hoppered structure; they are like little stairs. (See attached photo.) The problem with such a crystal structure is that they can only form inside the liquid fase and than the liquid bismuth has to be removed to reveal those hoppered structures. If the liquid is not removed in time, such hoppered structures are covered with other structures and then form a solid mass. I guess it would be rare for such a 'liquid removal' process to occur in nature, but has anyone of you ever seen a natural hoppered crystal of bismuth? Or would it be to unlikely to occur in nature this way?

[keldjarn]

Paul,
you will never find a natural specimen of Bismuth with the same perfect hopper-structure as is commonly seen in synthetic specimens. But crystal aggregates of native Bismuth from the classic locaklities in Enzgebirge, Saxony, Germany (Schlema, Pöhla etc) may exhibit natural hopper-growth and also dendritic feather-formed aggregates.
Knut

[bugrock]

Hello,

Look up this topic on the forum: https://www.mineral-forum.com/message-board/viewtopic.php?t=801

The images are of natural native bismuth. Some of the crystals approach the lab made ones but as has been said, not so perfectly formed.

[Paul S]

Thanks for the tip about the bismut crystals. They are clearly wonderfully crystalized specimen. I'm not sure however wether the crystals are really hoppered or just show their crystal faces in a way that resembles hoppering. I guess a good close-up photo of one of such crystals would be the best way to judge.

And of course the hoppering of natural crystals will never be as good as the synthetic ones, let alone their colours. The dendritic growth is interesting, for I have a few synthetically grown dendritic structures myself. I guess I'll be looking for some natural dendritic bismuth crystals in the future to add to my collection, thanks for sharing that information!

[bugrock]

Actually I think there is hoppered [or at least "stepped" growth on some of these pieces but it is in a crude form where you have to "fill in the blanks" so to speak. This is my impression and I am not a an expert on crystal growth by any means but perhaps someone else in this forum can explain the formation of bismuth xls in detail. Mindat does have some images that show stepped growth. I suspect under natural conditions the concentration of bismuth in solution varies with time and layers are added and then mobilized away resulting in erratic and asymmetric growth.

Actually I think these pieces are more interesting unless you insist on symmetric art forms.

Is this type of xl growth/dissolution similar to what occurs in some cubic fluorite?

The color is another subject and I do not know why the lab grown pieces have those colors. Is it surface oxidation as occurs in copper or some other impurity resulting from the way lab xls are produced? If you cut into one of the lab pieces would it show the same colors?

See the following mindat images:

https://www.mindat.org/photo-83358.html

https://www.mindat.org/photo-41057.html

https://www.mindat.org/photo-41056.html

https://www.mindat.org/photo-169952.html

https://www.mindat.org/photo-219891.html

https://www.mindat.org/photo-280822.html

https://www.mindat.org/photo-48805.html

https://www.mindat.org/photo-47714.html

[Paul S]