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Unknown mineral from Erongo mountains
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Pierre Joubert




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PostPosted: Mar 16, 2017 09:45    Post subject: Unknown mineral from Erongo mountains  

I found these small crystals of up to about 1.5 mm long on a specimen of Fluorite with albite. i have tried my best to find out what it is but to no avail. The small crystals have a yellowish colouring with plenty of flaws. They are too small to do futher tests on or to describe the shape.


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PostPosted: Mar 16, 2017 10:02    Post subject: Re: Unknown mineral from Erongo mountains  

Can you discern the crystal system? Some photos appear hexagonal others monoclinic or triclinic.
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PostPosted: Mar 16, 2017 10:32    Post subject: Re: Unknown mineral from Erongo mountains  

John Betts wrote:
Can you discern the crystal system? Some photos appear hexagonal others monoclinic or triclinic.


Hi John, I can only guess monoclinic - prism.

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PostPosted: Mar 16, 2017 10:40    Post subject: Re: Unknown mineral from Erongo mountains  

Isn´t it Brazilianite??
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PostPosted: Mar 16, 2017 11:01    Post subject: Re: Unknown mineral from Erongo mountains  

braulioff wrote:
Isn´t it Brazilianite??


There is definitely a resemblance.

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PostPosted: Mar 16, 2017 11:38    Post subject: Re: Unknown mineral from Erongo mountains  

Photo P1250731.JPG looks like a feldspar...
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PostPosted: Mar 16, 2017 11:56    Post subject: Re: Unknown mineral from Erongo mountains  

Could be Apatite
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PostPosted: Mar 16, 2017 12:02    Post subject: Re: Unknown mineral from Erongo mountains  

Enrique Llorens wrote:
Could be Apatite

Good try Enrique.

Assuming that it comes from a pegmatite, Fluorapatite looks as a good probability. See this other one from a pegmatite: https://www.mindat.org/photo-108173.html
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PostPosted: Mar 16, 2017 12:12    Post subject: Re: Unknown mineral from Erongo mountains  

Enrique Llorens wrote:
Could be Apatite


Is the prism six-sided?

It looks a four-sided prism with smaller secondary edge faces making a total of eight prism faces. If true that would eliminate apatite.

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Pierre Joubert




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PostPosted: Mar 16, 2017 14:06    Post subject: Re: Unknown mineral from Erongo mountains  

John Betts wrote:
Enrique Llorens wrote:
Could be Apatite


Is the prism six-sided?

It looks a four-sided prism with smaller secondary edge faces making a total of eight prism faces. If true that would eliminate apatite.


Your observation appears to be correct. I noted some of the smaller crystals (minute) that has a shape similar to herkimer diamond. I also noted very eratic flaws. The specimen on which these small crystals sit, is too large to place under a microscope.

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PostPosted: Mar 16, 2017 14:29    Post subject: Re: Unknown mineral from Erongo mountains  

minerals from erongo: https://www.mindat.org/loc-21818.html

maybe give it a try under long wave and short wave UV

Also, check inclusions under the microscope:
-any cleavages planes through the crystals, and if so how are they oriented?
-any parallel growth tubes inside the crystal?
-any doubling seen when looking through the crystal (i.e. doubling of the facets, fractures, inclusions, contacting matrix)?

Then, all you're left with for identification would be crystal shapes, and paragenesis (if you could identify all other present minerals/rock).
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PostPosted: Mar 16, 2017 16:26    Post subject: Re: Unknown mineral from Erongo mountains  

cascaillou wrote:
minerals from erongo: https://www.mindat.org/loc-21818.html

maybe give it a try under long wave and short wave UV

Also, check inclusions under the microscope, notably look for cleavages planes. Maybe parralel growth tubes too?

Then, all you're left with are the crystal shapes and paragenesis.


I found another specimen also with the same crystals, perhaps easier to photograph. I will try tomorrow.

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PostPosted: Mar 16, 2017 17:20    Post subject: Re: Unknown mineral from Erongo mountains  

Herderite?
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PostPosted: Mar 16, 2017 17:45    Post subject: Re: Unknown mineral from Erongo mountains  

I was thinking of herderite as well. Some of the crystals resemble crystals I have from Portuguese pegmatites.

Best regards,

Felix

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PostPosted: Mar 16, 2017 19:38    Post subject: Re: Unknown mineral from Erongo mountains  

herderite/hydroxylherderite was also my bet (after I checked the list of minerals from Erongo), however there could be other possibilities (and not necessarily found on that list), so let's wait for a few more observations (I've suggested a few visual tests in my previous post).
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PostPosted: Mar 17, 2017 07:43    Post subject: Re: Unknown mineral from Erongo mountains  

marco campos-venuti wrote:
Herderite?


Hi Marco, looking at some photos, you and others may be right. Please look at this photo from a Rob Lavinsky specimen https://www.mineralienatlas.de/lexikon/index.php/Bildanzeige?pict=1257873742

Here are a few more photos. I also want to thank everyone for their input. Can I ask Jordi or staff to change this topic to 'Unknown minerals from Erongo Mountains', as I have a few more to show from another specimen.



P1250800.JPG
 Locality:
Erongo Mountain, Usakos, Erongo Region, Namibia
 Description:
Possibly Herderite on albite and fluorite
 Viewed:  3153 Time(s)

P1250800.JPG



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PostPosted: Mar 17, 2017 07:47    Post subject: Re: Unknown mineral from Erongo mountains  

A few more pictures of the last specimen.


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The white crystals could be albite.
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PostPosted: Mar 17, 2017 07:50    Post subject: Re: Unknown mineral from Erongo mountains  

cascaillou wrote:
minerals from erongo: https://www.mindat.org/loc-21818.html

maybe give it a try under long wave and short wave UV

Also, check inclusions under the microscope:
-any cleavages planes through the crystals, and if so how are they oriented?
-any parallel growth tubes inside the crystal?
-any doubling seen when looking through the crystal (i.e. doubling of the facets, fractures, inclusions, contacting matrix)?

Then, all you're left with for identification would be crystal shapes, and paragenesis (if you could identify all other present minerals/rock).


I am sorry Cascaillou, but as I pointed out, the specimens are to large to view under a microscope.

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PostPosted: Mar 17, 2017 08:25    Post subject: Re: Unknown mineral from Erongo mountains  

Pierre Joubert wrote:
A few more pictures of the last specimen.

With the last pictures I agree with my colleagues about Herderite Group.
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PostPosted: Mar 17, 2017 12:24    Post subject: Re: Unknown mineral from Erongo mountains  

I was also thinking of scapolite
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