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PhotosBertrandite - Kara-Oba W deposit, Betpakdala Desert, Karagandy Province, Kazakhstan

10th Aug 2017 00:28 UTCRichard Gunter Expert

Bertrandite, Smoky Quartz, Pyrite

Kara-Oba W deposit, Moiynkum District, Jambyl Region, Kazakhstan

Are you going to check out the Betpakdalite? I have rounded, 2 mm, yellow-green rhombohedrons with notably high IR on the surface of my posted Kara Oba Cosalite-Quartz sample. I thought they were unusual Siderite but it might not be the case if Betpakdalite occurs in that paragenesis.

10th Aug 2017 02:15 UTCPavel Kartashov Manager

Hi Richard,

where do you see betpakdalite in caption or at the photo? It grows in quite different association in this deposit - forms microcrystalline pseudomorphoses after pyrite in muscovite greisens. Betpakdalite never was observed in axial cavities and pockets of ore veins with fresh sulphides.

10th Aug 2017 15:27 UTCRichard Gunter Expert

Hi Pavel:

Betpakdalite is mentioned in the photo caption as a possible identification of the powdery yellow material. Would the rounded rhombs on my quartz crystal be Siderite , as I originally thought?

10th Aug 2017 17:45 UTCPavel Kartashov Manager

Yes, I undersood at last.

This yellow stuff over the sample is rather iron oxalate precepitation after cleaning of the stone in oxalic acid, then any betpakdalite.:-) No real betpakdalite is possible in such samples.

10th Aug 2017 18:16 UTCRichard Gunter Expert

Hi Pavel:

Thanks for the information. As far as I can tell my sample has not been cleaned and the late-stage yellow phase is definitely crystalline.

10th Aug 2017 18:36 UTCUwe Kolitsch Manager

An anthropogenic iron oxalate would coat all crystal faces, not only specific ones (gravitational influence).

Message sent.

10th Aug 2017 19:05 UTCPavel Kartashov Manager

Iron oxalate may to be quite crystalline - this is function of time spent by the sample in solution before its final washing.

Uwe, you discoursing as Chinese scholar, who never cleaned samples by oxalic acid personally. :-)

Different minerals in the same association has different quality of their surfaces. Iron oxalate able to be eliminated from quartz smooth surface by hard brush, but bertrandite surface is more rough (etched, porous or covered by some insoluble porous film) and catching oxalate particles more tightly.

11th Aug 2017 08:18 UTCMartin Slama Expert

Hi Pavel,

due to the fact that I am not sure what it is, I wrote possibly. What could it be? The Pyrite is fresh and the Bertrandite xls are covered with this yellow stuff, no xls are shown.

11th Aug 2017 12:21 UTCPavel Kartashov Manager

Rodochrosite-siderite series minerals are sometimes very abundant in this association. They oxidizing more readily than pyrite. So even fresh pyrite here able to be covered by crusts of Fe-Mn hydroxides.

I am think that this yellowish dirt is traces of unsuccessful cleaning in oxalic acid solution. Exactly this effect is the reason why I don't use it over 20 years.

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