Grand Praz is an ancient cobalt and nickel mine in the Val d’Anniviers. The ore appears in dolomitic veins in an amphibolic host rock. The sample shown here was taken in level 5 of the mine. It is one of the rare samples containing nickeline.
Polished slab. Width: 5 cm:
Enlarged part of the foto above showing the nickeline and a silver unknown mineral:
The polished sample only contains nickeline and a white ore mineral difficult to determine. Since the reflectivity at 680 nm is about 57% while the mineral shows no anisotropy it is most likely gersdorffite. Nic //, Obj. 20x, air, scale bar: 100 µm:
Here is a series of photos showing the anisotropy of nickeline (Nic //, Obj. 20x, air, 100 µm scale bar):
For further informations on the region this PhD thesis might be interesting:
Meisser, N (1990): Etude minéralogique des gîtes métallifères au sud-est d'Ayer (Val d'Anniviers, Valais, Suisse): paragenèses remarquables à Ni-Co-Bi-As, Cu-Bi-Co, Cu et à U-Terres rares