FMF - Friends of Minerals Forum, discussion and message board

[Bob Carnein]

The specimen shown in the photos has been in my collection for over 40 years. It came from a collection that, unfortunately, had become pretty badly mixed up. The label that came with it called it "Hematite, Dognacska, [Dognecea] Hungary, twinned on c (0001)". I accepted that until I saw a very similar (but larger) specimen at the Sept. 2021 Hard Rock Summit show in Denver. That specimen was identified as "Rutile pseud. after Ilmenite, Binn Valley, Valais, Switzerland". Because the specimen doesn't look like Dognecea hematites on Mindat, I would like any input FMF members might be able to provide. I believe the transparent brown mineral intergrown with one of the larger crystals may be anatase, but that's little more than a guess. The matrix is a micaceous gneiss, and associated minerals include quartz and what appears to be adularia. Thanks for any input!

[Roger Warin]

Hi,
I have a specimen of geocronite that I think looks like.
Origin: Binental, Lengenbach Quarry, Binntal, Wallis, Switzerland.
The rock is a Sacaharoid dolomite.
The brown chip is sphalerite, I think.

[Brent Lockhart]

I wonder if it is Rutile. It is hard to exactly tell if that is a possibility from the photos, but it would fit with the gneiss matrix. There are multiple Swiss localities for Rutiles on gneiss, such as Iragna in Ticino. The brownish mineral is a bit harder to distinguish, so I'll pass on that. I you want to be sure, xrd is very cheap to do these days.

[Volkmar Stingl]

What is the streak color and hardness?

Volkmar

[Gerhard Brandstetter]

Interesting alpine specimen!
For sure not Hematite, from Dognacska, [Dognecea] Hungary. I own some.
Crystal forms can be very different and crazy here, but matrix is wrong and in the Banat samples we do not see Anatase, Rutile and Adularia.

My guess would be Hematite with Rutile from Binn Valley, CH.
I have a miniature with a similar combination.
That could fit. But a guess only....

[Pete Richards]

M vote is for this being from Binn Valley (Binntal), but not Lengenbach Quarry. The matrix is poorly shown but looks reasonable for Binn. The blocky dark grey crystals have a reasonable hematite morphology. Whether they have been pseudomorphed or not cannot be determined from the photos. The brown translcent/transparent crystal is morphologically consistent with anatase, which is common (in many habits) in Binn and surrounding mountains.

So it all seems to fit with Binn Valley. But it could also be from some other locality, too.

[Bob Carnein]

Thanks for all of the suggestions. I forgot to mention that the crystals are somewhat magnetic (with an ordinary magnet). The specimen I saw at Denver was so expensive that I didn't want to try any destructive tests (i.e. streak).

[Jordi Fabre]

[alfredo]

"Dognecea it was in Hungary but currently is Romania"

Some parts of Hungary are now in Slovakia and Serbia. One Hungarian mineral collector likes to say, "Hungary is the only country surrounded by itself". ;)