Atoll Texture in Minerals of the Cobaltite-Gersdorffite Series from the Raipas Mine, Finnmark, Norway
Particularly fine examples of “atoll-texture” are shown by Co-Ni-Fe-(Cu) sulpharsenides in specimens from the disused Raipas mine near Alta, Finnmark, northern Norway. Reinvestigations by optical, electron microprobe, and X-ray diffraction techniques have shown that the atolls, and the grains from which they appear to have developed by core replacement, are composed of two mineral phases. One, with a general composition (Co,Ni,Fe,Cu)3As2S4 can be shown to be a Co-rich member of the cobaltite-gersdorffite series; the other phase, (Co,Ni,Fe,Cu)2AsS2, does not appear to correspond to any reported natural mineral having this general composition.
The nature of the often spheroidal grains from which the atolls have developed is not too certain. They bear certain resemblances to the general class of framboidal textures, though their compositions and internal structures are unusual.
KeywordsElectron Microprobe Econ Geol Copper Sulphide Native Silver Great Bear Lake
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