FMF - Friends of Minerals Forum, discussion and message board

[Cesar M. Salvan]

Cechite is a rare lead-iron vanadate, first described in samples from Alexander mine and the Posepny vein, at Vrancice (Bohemia, Czech Republic) Apart of the scarcity of the mineral, it is not very interesting for collectors (apart of systematic collectors), because it normally occurs as small granular masses or very small, black or dark brown, equant crystals. It's easily confused with goethite when massive and with mottramite or descloizite when it forms crystals. Probably some occurrences have been overlooked due to these similarities.

Cechite gained interest with the finding of very good crystals at the Santiago Mine (María Magdalena Mine), in Ulldemolins (Tarragona, Catalonia, Spain) by collectors from the GMC (Grup Mineralògic Catalá), where it forms well-formed euhedral crystals, usually on fluorite, forming beautiful specimens (for the species).

This is a good opportunity to observe and describe the Raman spectrum of this mineral. Raman spectroscopy is the ideal technique for the fast, reliable and non-destructive identification of vanadates and arsenates of the descloizite-adelite group, even when it forms minute crystals, but the Raman spectrum of cechite was unknown.

I used the good cechite from Ulldemolins to study its spectrum and I decided to publish the result here to spread its spectrum as much described as possible, in order to aid in future identifications of the material. Also, I want to share an interesting feature of the cechite from Ulldemolins: the occurrence of copper-rich crystals, whose study, as far as I know, does not match with any described species. This suggests an interesting structural problem or even a new species.

I present the description here and maybe somebody could add to the discussion, identify mistakes or collaborate to further study the structure and the potential identification of the specie(s) present:

To see this column you have to click on this link or the image:

[Cesar M. Salvan]

More images of the interesting cechite with the undefined copper phase (maybe a new mineral?) from Ulldemolins.

In the samples are also present the descloizite-mottramite series, which forms green, very small crystals.

[Peter Lemkin]

Photo 2016-12-28 21-25-47 certainly shows nice xx. I've collected at Vrancice and seen specimens at local Czech shows, but they were always 'black-uglies' without any euhedral xxm to my memory. I'd have to go back to the Mineral Museum to see if they have anything better, but it is currently closed for renovation.

[Cesar M. Salvan]

[Jordi Fabre]

[Cesar M. Salvan]

[Joan Rosell]

We started studies on the cechite in July 2015. The first analysis we made showed the presence of Cu in the SEM-EDS spectra. But we studied inside broken crystals. In those crystals, Cu was a thin layer on the surface (less than 20 um). We have made several analyses from different crystals and Cu was only present on surface. We have also analyzed some crystals with EPMA and results are totally consistent with values acquired by FE-SEM-EDS.
On Ulldemolins cechite crystals it is usual to find other mineral species on the surface, like mottramite or, more rarely, calderonite.
We have also a LIBS spectra made by Adolf Cortel and different RAMAN spectra those show similar structures like pyrobelonite-descloizite-mottramite. That's why only RAMAN is incomplete to confirm species.
We are working on other analyses and studies and preparing an article (as indicated in mindat Ulldemolins page) for the next magazine of Grup Mineralògic Català. It would have been great if you had contacted us in order to discuss the results. But never is too late...