FMF - Friends of Minerals Forum, discussion and message board

[Roger Warin]

Hello
Here is a very rare mineral, so much so that Mindat is unaware of its Mexican origin.
It is in Mexico that Henri Ungemach found it, but where?

[Jordi Fabre]

Considering the time when the sample was found, it occurs to me that it could be from the El Doctor area in Querétaro, and that it might not be Moschellandsbergite but rather Tiemannite.
If the sample could be analyzed without damaging it, it would be interesting to see if it is indeed Moschellandsbergite...

[lluis]

Taking in account that it is in a museum, that a simply test in a test tube would say if selenium is there, so, I suppose that it has not been found, so, no Tiemannite, and if Moschellandsbergite, could not be from Naica mine? It has mercury and silver, so, Moschellandsbergite could occur (or be an antropogenic product, who knows?)
With best wishes

Lluís

[Roger Warin]

This sample must have been collected in 1907-1908.
My respect for Ungemach is immense. He could not have been mistaken.
He was the main associate of Georges Friedel in Strasbourg.
He gave his collection to Joseph Donnay, one of the greatest crystallographers of the last century. Donnay was Belgian, born in Liège, but he worked all his life in Canada and the USA with the greatest.
His crystallographic drawings were directly included in the results of the young RX technique.
I photographed this specimen in 2013. My current memory is based on my photo. The crystal is not dull as the entire photo shows me, which is difficult to take. It has faces very far from sulfides, more like chalcopyrite, more reflective. I can retake this photo with my current, more efficient equipment.
To answer Jordi, I would say that the appearance of the surfaces does not correspond to black and dull crystals, but above all the morphology of the crystal is different from the sphalerite group: it cannot belong to the sphalerite class.
That said, I can ask Frédéric to prove my answer. And I can take a better photo. Frédéric can also provide an answer on the origin. I do not have access to the Ungemach documents.
This mineralogy of heavy atoms is remarkable because the nature of the bonds loses the ionic character to introduce a covalent component.
I remain convinced of the validity of Ungemach's identification.
To be continued, maybe.