See the below attachment. I have a yellowish mineral (at the bottom of each photo). For sure it is not Pyrite, and Chalcopyrite (which in the same sample, appears more yellow). This mineral shows anisotropy.
Any ideas?
It is really difficult to determine the mineral only by photo. It should be better to know more about ores, relationships with other minerals, optic properties etc. maybe it is mawsonite, Cu6Fe2SnS8, or other minerals from stannite family...
Thanks for your opinion. For the bornite the anisotropy is weak > absent, and in my case is at least good (I think). Also, I have doubts about the color. For the bornite the color is pinkish-grey/brown, and in my case tends to a yellowish color. Many thanks, it's a good start for now.
I agree with T. Evstigneeva, it is hard to determine just by a picture. But do any of your other samples contain pyrrhotite? If so, compare that with the other pyrrhotite. Also how strong is the anisotropy?
I am also think it seem look like Troilite or pyrrhotite. But for sure please tell us some mineral association
I agree with the replies above regarding the dangers of identification by photo. But to my mind and judging by the saturation, hue and brightness of the identified minerals bournonite and galena, it cannot be bornite or pyrrhotite or stannite or any of the strongly coloured minerals. It is more likely to be a sulphosalt of some kind.
The sample is from a Cu-Au-Te ore deposit, and in this plate the predominant minerals are Galena, Sphalerite, Pyrite, Chalcopyrite, Sulphosalts (Bournonite, Tetrahedrite), and for the gangue mineral the predominant is Q. See the bellow photo to see another grain.
At this moment I didn't made a chemical analysis on this mineral.
Thanks to all for patience and support.
It is very difficult to recognize just looking at pictures. But if the mineral in question has a brownish tint can probably be a esfarelita rich in iron, which can introduce anisotropy and light brown internal reflections. See Paul Ramdohr - The ore minerals and Their intergrowths
It is very difficult to recognize just looking at pictures. But if the mineral in question has a brownish tint can probably be an iron-rich sphalerite, which may exhibit anisotropy, as well as light brown internal reflections. See Paul Ramdohr - The ore minerals and Their intergrowths
It can be seen from your latest digital image that the unknown mineral has a "reflectance" (ignoring possible bireflectance or reflectance pleochroism) roughly between that of bournonite and that of galena. Just looking at the luminance key in the Quantitative Data File for Ore Minerals, galena has Y% of c.43-44, bournonite Y% of 34-36% and a host of sulphosalts such as jamesonite Y% 36-44, boulangerite Y% 37-42, zinkenite 37-42, meneghinite 37-43, geocronite 39-42 etc etc. I do not think it is nagyagite which is weakly anisoropic Y% 40-42 and which might be expected in your Au-Te deposit.
Thank you all for your opinions. I will make further investigation, probably with a SEM-EDX analyses.
I will post another photo in a new post, I hope don't bother you.
Reflectivity is inadequate. That we concede. While I agree with the possibilities, which are relatively few, an SEM should also do the trick. I would be curious to know what it turns out to be.
Thank you for the answer and for your kindness, the sample was sent for an EMPA analysis.
For those who are still curious about the mineral(s) from the reflected light images: hessite, petzite and stutzite. Thanks for all suggestions!
Probably there are other Au-Ag tellurides [...]
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