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Question about an old specimen
  
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Bob Carnein




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PostPosted: Sep 26, 2021 16:54    Post subject: Question about an old specimen  

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!


IMG_0140 (2).JPG
 Mineral: Hematite
 Locality:
Dognecea, Banat Mountains, Ocna de Fier-Dognecea District, Caraș-Severin, Romania
 Dimensions: 7 x 4.5 x 4 cm
 Description:
 Viewed:  648 Time(s)

IMG_0140 (2).JPG



IMG_0145 (2).JPG
 Mineral: Hematite
 Locality:
Dognecea, Banat Mountains, Ocna de Fier-Dognecea District, Caraș-Severin, Romania
 Description:
 Viewed:  646 Time(s)

IMG_0145 (2).JPG


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Roger Warin




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PostPosted: Sep 26, 2021 21:38    Post subject: Re: Question about an old specimen  

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.



Geocronite5041_R.jpg
 Mineral: Geocronite
 Locality:
Lengenbach Quarry, Fäld, Binn Valley (Binntal), Wallis (Valais), Switzerland
 Description:
Gauthier's specimen
 Viewed:  585 Time(s)

Geocronite5041_R.jpg


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Brent Lockhart




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PostPosted: Sep 26, 2021 22:35    Post subject: Re: Question about an old specimen  

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.
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Volkmar Stingl




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PostPosted: Sep 26, 2021 22:49    Post subject: Re: Question about an old specimen  

What is the streak color and hardness?

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Gerhard Brandstetter




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PostPosted: Sep 27, 2021 02:30    Post subject: Re: Question about an old specimen  

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....
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Pete Richards
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PostPosted: Sep 27, 2021 09:08    Post subject: Re: Question about an old specimen  

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.

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Bob Carnein




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PostPosted: Sep 27, 2021 09:39    Post subject: Re: Question about an old specimen  

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).
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Jordi Fabre
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PostPosted: Sep 27, 2021 10:27    Post subject: Re: Question about an old specimen  

Bob Carnein wrote:
Mineral: Hematite
Locality: Dognecea, Hungary
Dimensions: 7x4.5x4 cm


Well first of all, Dognecea was in Hungary but it is currently in Romania 😉

Dognecea is a name for an area including the small village of Dognecea and the famous mines of Ocna de Fier, the type locality of several species including the Veszelyite. What I mean, is that currently is an abandoned mining area something forgotten but it was very rich in the past giving many different mineral species. The material could very well be Hematite, and Ocna de Fier is well known for the diversity of their Hematites.

I would not discard totally 'Dognecea-Ocna de Fier' for this piece. The best thing to do is order an analysis of it and if Hematite, why not 'Dognecea-Ocna de Fier'?. Of course if at the analysis it appears Rutile or Anatase also, then not 'Dognecea-Ocna de Fier'
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alfredo
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PostPosted: Sep 27, 2021 11:17    Post subject: Re: Question about an old specimen  

"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". ;)
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