Manganoan calcite?

Hi all,
I have a calcite specimen, coming from Hunan, which is of a pastel pink colour. This is the photo: [www.mindat.org] This specimen shows a strong pink-orange fluorescence both under long-wave UV and short-wave UV. Could these two proofs (provenance and fluorescence) be sufficient to affirm that this is manganoan calcite? Moreover some Robert Lavinsky's manganoan calcites are like my specimen. What do you think about?

Thanks in advance,
Luca



Edited 1 time(s). Last edit at 09/06/2008 05:16PM by Luca Toffolo.

It's probably Mn-bearing, but how much...?
It's the old problem with variety names: Does one call it manganoan if it has 500 ppm Mn? 0.5 wt.%? 1, 5, 10... wt.%?

Thank you Uwe, I've understood. I had just hoped for a qualitative test... It doesn't matter... When I can, I will execute a precise analysis.

Best regards,
Luca

P.S. Do you know the exact percetage in Mn that a calcite must bear to be considered Manganoan?

Hi Luca, I agre with Uwe, near to where I live I can find piles of light pink coloured calcite, but I only class them as "Calcite".

Spencer.

Thank you, Spencer. I will consider my specimen as simple pink calcite.

Luca

According my poinion, is a simply calcite with a poor percent of Manganese... i found some veins of this calcite in Friuli, and i classified them under calcite

I'm not exactly sure what percentages are required for these to work, but there are several simple qualitative tests for Mn.

One involves heating the (powdered - break off a few mg from the back) mineral with sodium carbonate and potassium nitrate - a greenish-blue bead will form (containing manganate), and this will turn purple when dissolved in dilute acid (the manganese disproportionates to permanganate and MnO2). Source: http://www.crscientific.com/newsletter-march2003.html


Another involves heating the mineral with borax until it fuses - if done in the oxidizing portion of a gas flame, the bead will be purple (http://chemistry.about.com/library/weekly/aa010102a.htm).

Another test that would not be specific to manganese but would indicate the presence of metals other than calcium (and is probably more sensitive than the other tests) would be the dissolution of a piece of the mineral in HCl, followed by the addition of sodium hydroxide solution. Magnesium will precipitate upon the addition of small amounts of hydroxide as white Mg(OH)2. Manganese will precipitate as brownish Mn(OH)2 (brown is apparently from Mn3+ resulting from air oxidation). Calcium hydroxide might precipitate if too much sodium hydroxide is added, but it is fairly soluble.

Thank you for the informations, NH. I think that I will try the third method, first (more feasible with the means I can have).

Best regards,
Luca

thank you all for the information,thank you all for taking your time to explain,i am gratefull for it,,i have one i have been wondering about,,one photo is the back and another is the front,this calcite has come from las minas, veracruz.,,,,,,ab

This one looks more like baryte to me.

wow,peter, if she says baryite,its baryite,thanks,,,ab