FMF - Friends of Minerals Forum, discussion and message board

[Elise]

We have a question about cobalt calcite such as Jordi posted above https://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: https://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: https://www.mindat.org/photo-142150.html . I thought I saw blades, nothing as beautiful as this however: https://www.mindat.org/photo-186107.html . More like this: https://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

[Elise]

[javmex2]

Some from Mexico.

[am mizunaka]

A few more examples.

[am mizunaka]

[mihailovici79]

Calcite from Romania:

[alex chaus]

Hi, all.
Some contribution to calcite theme from Kyrgyzstan. All images provided are from the same location - Tereksay stibnite mine, collected at different levels during 80th to 2000 years. rusty film on some crystals is iron oxide hard to remove (any advise how to?). Sorry for images bad quality they are just from my catalog.
Alex

[GneissWare]

[alex chaus]

Thank you, Bob, I'll try to find or get it from somewhere abroad.
Alex

[Elise]

The "Calcite (complicated shape) Tereksay mine" specimen is very interesting!

Below is a neat specimen I've been trying to photograph. It has copper inclusions just under the surface which sparkle in the light, no luck showing that here yet. Some of the inclusions stick out of the faces. This is from Hancock, MI.

Cheers,
Elise

[Elise]

and one more - I was trying to capture the curved growth features on the crystal faces; turned into blow-out areas, but more or less shows it. This is from Sweetwater Mine, MO. The calcite is on galena, but the latter is not visible in this view.

Elise