FMF - Friends of Minerals Forum, discussion and message board

[Guido Mazzoleni]

Ciao a tutti.
Cerco informazioni sulla calcite di Madan (Bulgaria): ho comperato un bel campione di calcite scalenoedrica rosa, proveniente da Madan, etichettata come "cobaltoan calcite". Il campione è molto fluorescente, circa con la stessa intensità e lo stesso colore (rosato intenso/arancio) sotto UV onda lunga ed onda corta. Il cobalto è elencato tra gli elementi inibitori (quenchers) della fluorescenza. Chi sa qualcosa di analisi di questo tipo di calcite? Oppure, semplicemente, sa dell'esistenza di "cobaltoan calcite" a Madan?
Grazie mille.
Guido

[Jordi Fabre]

Caro Guido,

People tends to use "cobaltoan calcite" for all kind of pink Calcites although them are many times manganoan, iron rich, or just pink Calcites without traces of anything (excepting Calcium) ;-)

I never analyzed the Madan Calcites, so I can't tell you if it is some manganese or other(s) trace(s) on these specimens, I'm sorry.

Jordi

[lluis]

Caro Guido

I agree completely with Jordi in the incorrect use of the name.
I think to remmeber to have seen them labeled as manganoan calcites.

I think that you could do some tests to get an idea of what is (or of what is not :-) )

Take a small chip of the calcite, in any part that do not damage the piece.
Dissolve in an acid (clorhidric or nitric). CAUTION: ACIDS AND REACTIVES ARE POTENTIALLY DANGEROUS. SO, USE GLOVES, PROTECTION GLASES, ETC, ETC....)

Neutralize with ammonia
Add some drops of potassium tiocyanate.
A red color means Iron
A blue color , extractable with acetone, means coblat
Manganese is distinguishable passing hydrigen sulphide by the neutralized solution (precipitate of salmon colored manganese sulphide), if the others are not present.

Hope that that helps

With best wishes

Lluís

[lluis]

Jordi is completely right!

I am still seeing cobaltian dolomites from Shaba labeled as cobaltian calcites, despite the already "old" article published in MR about that thema....

With best wishes

Lluís

[Carles Curto]

There is an historical confussion about cobaltian Calcite and Sphaerocobaltite (the old Cobaltocalcite). For years, and as species, Cobaltocalcite (not cobaltian Calcite) was the same as the actual Sphaerocobaltite and it is obviously, the origin of the mistake.
Sphaerocobaltite (cobalt carbonate) is in calcite series, with very similar structure and crystallization. On Shaba (or Katanga), both species coexist, Sphaerocobaltite, deep colored and generally forming rhombohedral crystals and Calcite (cobaltoan) that forms scalenohedrons of good color but usually not so deep as Sphaerocobaltite.
But there is an added complication! On Shaba, some rhombohedral calcites are clearly zoned and its most external band can be (only an accurate analysis can solve the doubt) Sphaerocobaltite.

[Guido Mazzoleni]

Dear Lluìs,

many thanks for your kind reply. I will ask for some help from a friend who certainly will have all needed chemical products, in order to execute the test you suggested. Maybe we will need some time to do it, anyway I will be happy to let you know the results.

Grazie mille, ciao!

Guido

[Guido Mazzoleni]

Dear Carles,

many thanks to you too. As for zoned growth of the crystal, in the specimen I bought, the only thing I am able to say is that the fluorescence looks perfectly homogeneous, with a soft diffusion appearance due to the transparence of the crystals. It is probably one of the most beautiful fluorescing piece in my small collection.
Probably the best key to understand is knowing the geological context and the complete mineralogy of Madan district ore bodies. I read something about manganoan calcite from a more precise locality, the Androvo Mine in the nearby Zlatograd district.

Grazie mille, ciao!
Guido