FMF - Minerals Forum, discussion and message board

[John S. White]

These photos of the same piece probably show the poker chip habit better. This is from the Fozichong lead & zinc mine, Guangxi Province, China, and is 11 cm across.

[Jordi Fabre]

A funny one

[Jordi Fabre]

An oddity

[Tobias Martin]

When talking of oddities, here once again pictures of the calcite from Holzen quarry, North Rhine-Westphalia, Germany. See the last pages of my collection thread for further pictures and information about this specimen.

[am mizunaka]

Another calcite from the Roncari Quarry.

[Jordi Fabre]

A beauty, isn't?

[Tobias Martin]

[Paul Bordovsky]

I finally got around to shooting some new pics, and here are some calcites to add to this thread.

[Paul Bordovsky]

I thought I'd add a few calcites local to the central Texas area, around Austin.. All are from Travis county, Texas, USA.

[Tracy]

Finally I had a bit of free time and can contribute one of my own specimens! The lighting isn't ideal and doesn't show that the entire piece is white. I'm not sure exactly form these crystals have (there appear to be 5 sides to each crystal) but because the main crystals are very elongated they impart a "flower-like" the appearance to the specimen. From Daye Copper Mine, Daye Co., Huangshi Prefecture, Hubei Province, China. Size is about 13.5 x 7.5 x 4 cm.

- Tracy

[Elise]

We have a question about cobalt calcite such as Jordi posted above http://www.mineral-forum.com/message-board/viewtopic.php?p=12126&highlight=#12126
We have a druzy which goes by "cobaltocalcite" (and other names). But under magnification the crystals appear orthorhombic. Is there such a thing as "cobalt aragonite" which would have this same color, or are the crystals so distorted sometimes in the cobalt calcite that they would appear not to fit calcite's forms?

My understanding is that in the cobalt calcite the cause of the color is bivalent Co in the octahedral site causing the amazing pink color in Jordi's specimen; I was contrasting that with bivalent cobalt in tetrahedral coordination in spinel causing the blue of "cobalt spinel" (as an example of the same chromophore causing radically different color in different ion coordinations and taking that further into a discussion of geometry affecting absorption of light). Then someone pointed out to me that the druzy doesn't look like calcite, but rather the polymorph aragonite...which blew my whole mini-project out of the water. I went back to study aragonite and whether it occurs in this color and if so, whether cobalt could would be in the same location - but, I don't find any mention of aragonite with cobalt. So asking collectors.

I am trying to get a photomicrograph, but with no luck so far of getting enough detail - perhaps others have some images of cobalt calcite druzy to which I could compare what I have in hand.

As a total distraction, attached is an aragonite with cyclic twinning making it appear hexagonal. I am holding out for a pink calcite that appears orthorhombic....

Elise

[Elise]

uh oh, I am replying to my own post with belated insights from my collaborator - after looking at what I posted above, he wrote: "Well, I have spent the last hour or two looking at images of druzy (drusy) calcite and aragonite. The image you included on your inquiry looks nothing like ours. Everything about his druzy (Jordi's) says calcite, especially the rhombohedra. But here is a druzy-like pink aragonite: http://www.mindat.org/photo-142081.html . Don’t know if it is due to cobalt. Here is more pink druzy aragonite but not much like ours: http://www.mindat.org/photo-142150.html . I thought I saw blades, nothing as beautiful as this however: http://www.mindat.org/photo-186107.html . More like this: http://www.mindat.org/photo-35569.html . But then I went to drusy calcite and found images that look just like our specimen. One thing that makes me lean back toward ours being calcite is that the cleavage I observed in ours was what I would call perfect whereas , aragonite has imperfect cleavage. The only remaining problem with ours being calcite is the complete lack of rhombohedral crystal faces or rhombohedral cleavage – but that could simply be due to the way the crystals are all crowded into the site. Oh well, let me know what kind of feedback you get. I lean more toward it being calcite at this point."

Maybe now I can go back to my original project of cobalt calcite and cobalt spinel - but I would still enjoy seeing more examples of cobalt calcite and pink aragonite.

Cheers!
Elise

[kywawa]

Oh,god..it's too beautiful and attractive.

[am mizunaka]

Calcite within calcite crystals and the tiny tip of another poking out the top termination.

[nicu]

Hi,

I add here a few Calcites from my collection