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Mystery mineral from near Otanche, Colombia
  
  Index -> What is it? - Where is it from?
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Bergur_E_Sigurdarson




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PostPosted: Feb 19, 2019 18:01    Post subject: Mystery mineral from near Otanche, Colombia  

I acquired the following specimen in Bogota, and the seller told me it was from a mine near Otanche in the Western Emerald Belt (tho this town is close by Coscuez, that was not what was meant, and I travelled a few days later by Otanche as well as Coscuez, Peñas Blancs and Muzo, and in Otanche a couple of locals seemd familiar with the material)

It has the fairly typical dark gray shale matrix as well as some iron staining.
The whole thing is rather fragile and I haven't had opportunity yet to do a vinegar/acid test.

Most striking are the small seemingly botryoidal crystals of light but quite intense blue.
But I'm just not sure what they could be.

Each "sphere" is at most btw 1-2mm
The specimen in total 15,5cm x 7,5cm x 8,5cm



otanche-mystery-01.jpg
 Mineral: ?
 Description:
Otanche? , Colombia
15,5cm x 7,5cm x 8,5cm
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otanche-mystery-01.jpg



otanche-mystery-02.jpg
 Mineral: ?
 Description:
Otanche? , Colombia
15,5cm x 7,5cm x 8,5cm
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otanche-mystery-02.jpg


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John Betts




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PostPosted: Feb 19, 2019 18:22    Post subject: Re: Mystery mineral from near Otanche, Colombia  

What is the hardness?
What is the streak color?
Is there a cleavage?
Does it fizz with a drop of HCL acid?

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Riccardo Modanesi




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PostPosted: Feb 20, 2019 08:04    Post subject: Re: Mystery mineral from near Otanche, Colombia  

Hi to everybody!
Do you want a personal opinion of mine? Celestine!
Take it just as an opinion, without any other data!
Greetings from Italy by Riccardo.

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Hi! I'm a collector of minerals since 1973 and a gemmologist. On Summer I always visit mines and quarries all over Europe looking for minerals! Ok, there is time to tell you much much more! Greetings from Italy by Riccardo.
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Kevin Conroy




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PostPosted: Feb 20, 2019 09:26    Post subject: Re: Mystery mineral from near Otanche, Colombia  

John's right, some tests will definitely help narrow the field of possibilites. To me it looks like allophane, but I could be WAY off on my guess.
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Jordi Fabre
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PostPosted: Feb 20, 2019 10:05    Post subject: Re: Mystery mineral from near Otanche, Colombia  

Kevin Conroy wrote:
John's right, some tests will definitely help narrow the field of possibilites. To me it looks like allophane, but I could be WAY off on my guess.

Or in the Aluminium family, maybe Doyleite-Gibbsite. Analysis should tell it...
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Bergur_E_Sigurdarson




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PostPosted: Feb 20, 2019 10:23    Post subject: Re: Mystery mineral from near Otanche, Colombia  

Tests needed to be done of course :-)
(my bad)

I could rather easily part a sphere with my pocket knife.
So I figure the hardness is fairly low and could not see any cleavege pattern.
(Could the fact that the growths are botroidal be a factor in lack of cleavege visibility... at le3ast the smallness of each sphere sure is making it hard to see :-P )
Seemed to break randomly/concoidally.

No reaction to either oxalic acid or nitric acid (20%), which are the only ones I have access to at the moment.
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John Betts




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PostPosted: Feb 20, 2019 10:29    Post subject: Re: Mystery mineral from near Otanche, Colombia  

Does it scratch quartz? stilbite? calcite? (minerals I know you have...)
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Bergur_E_Sigurdarson




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PostPosted: Feb 20, 2019 10:58    Post subject: Re: Mystery mineral from near Otanche, Colombia  

I'm in Colombia, so I don't have my collection with me... but I do have quarts and calcite here and a definite no on the quartz and I would say no scratching on the calcite either, but there it's harder to tell.

I like Jordis suggestion of Doyleite-Gibbsite... tho I absolutely understand that my view of that is then only based on just that... a suggestion and viewing of photos of Doyleite-Gibbsite.
Would those not react to those acids?
(didn't see mention of acid reaction on Mindat)

I had been wondering about Allophane too.... but the few samples I've seen here of what I believe to be that are quite different (and I don't have the two I own with me to compare :-/ )
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Bergur_E_Sigurdarson




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PostPosted: Feb 20, 2019 11:26    Post subject: Re: Mystery mineral from near Otanche, Colombia  

FMA-2M5
On mindat are photos of Chinese Gibbsite that are particularly similar.
Also found other specimens using a Google image search.
Those results made me agree with Jordis suggestion :-)

(edited previous post, sorry for that)
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PostPosted: Feb 20, 2019 13:06    Post subject: Re: Mystery mineral from near Otanche, Colombia  

I believe that you're allowed to include links to Mindat to look at the photos, so please see these:

Doyleite https://www.mindat.org/min-1316.html

Gibbsite https://www.mindat.org/min-1689.html

Allophane https://www.mindat.org/min-139.html
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Bergur_E_Sigurdarson




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PostPosted: Feb 20, 2019 15:08    Post subject: Re: Mystery mineral from near Otanche, Colombia  

I did indeed look at those pages, and the specimen there that is most similar is this one:
https://www.mindat.org/FMA-2M5

I also realized I could do one more thing, I have a Convoy LW flashlight... and it does glow faintly neon-green.
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PostPosted: Feb 22, 2019 12:17    Post subject: Re: Mystery mineral from near Otanche, Colombia  

The blue botryoidal Chinese so-called "gibbsite" actually turns out to be mainly the mineral Evansite when you analyze them, so Evansite is another possibility to keep in mind for the Colombia material.
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PostPosted: Feb 22, 2019 12:54    Post subject: Re: Mystery mineral from near Otanche, Colombia  

https://www.mindat.org/621-JNT

https://www.mindat.org/WE3-6YF

...indeed... former link has both minerals attributed

I wish I could get it properly analyzed, but that will have to wait
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PostPosted: Feb 22, 2019 13:30    Post subject: Re: Mystery mineral from near Otanche, Colombia  

Sorry Alfredo I disagree... ;-)


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PostPosted: Feb 22, 2019 14:01    Post subject: Re: Mystery mineral from near Otanche, Colombia  

Then I suppose the material from there must be variable, Jordi. But analyzing 2 pieces from Rock Currier's collection and one from John Attard, all were evansite - Amorphous by XRD, and high phosphate content by wet chemistry and XRF.
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Bergur_E_Sigurdarson




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PostPosted: Mar 05, 2019 19:10    Post subject: Re: Mystery mineral from near Otanche, Colombia  

Today I got the opportunity to enter a small fragment from this piece to a lab here in Bogota (CEDTEC)
Not sure when results will be back... but looking forward to them and will of course post here once I get them :-D
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PostPosted: Mar 14, 2019 16:16    Post subject: Re: Mystery mineral from near Otanche, Colombia  

Just got informed by the lab that it's allophane
https://www.mindat.org/min-139.html
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