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Identifying adularia
  
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rocknroll




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PostPosted: Jun 21, 2018 09:58    Post subject: Identifying adularia  

Hi all,

I have quartz-adularia epithermal veins and am trying to identify the adularia phase. The quartz varies from milky to clear and they are difficult to decipher from one another.

I've read about SWIR UV lamps, however low temperature feldspars do not fluoresce crimson as high temperature feldspars do. I wanted to know if anyone knows of any good staining techniques and even possibly share their instructions? I'm not 100% keen on using HF. There's info online from the 1950s onwards and wondered if people are still using these techniques?

Thanks in advance.
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Pete Richards
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PostPosted: Jun 21, 2018 11:48    Post subject: Re: Identifying adularia  

If your specimens have well-formed crystals, there should be no problem distinguishing quartz from adularia. Look them both up on Mindat and look carefully at the shapes of the crystals. Also pay attention to cleavage characteristics.
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kushmeja




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PostPosted: Jun 21, 2018 12:04    Post subject: Re: Identifying adularia  

I agree with Pete, that if there are discernible crystals, that you should easily be able to tell the difference between the two based on appearance of the crystal structures alone.

Also, a simple hardness test should allow you to tell quartz from andularia, since quartz is harder than feldpar.
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Jesse Fisher




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PostPosted: Jun 21, 2018 12:18    Post subject: Re: Identifying adularia  

Adularia is a varietal name for orthoclase that has a simple prismatic habit. It is commonly found in alpine-type metamorphic rocks. If the material is fine-grained and/or does not show the adularia habit, it should be called orthocalse, or more simply, potassium feldspar (K-spar).

The staining technique that you mention is useful for differentiating k-spar from plagiocalse feldspars, but to my experience, is usually done with petrographic thin sections, and not hand specimen. If you do not have access to thin section making equipment and a petrographic microscope, x-ray diffraction is an easy way to confirm the presence of orthoclase. I believe there is at least one fellow offering this service to collectors, who advertises on Mindat.



Adularia-b2.jpg
 Mineral: Orthoclase with actinolite
 Locality:
Maderanertal, Uri, Switzerland
 Dimensions: fov=5cm
 Description:
Twinned adularia with fibrous actinolite (byssolite).
 Viewed:  1616 Time(s)

Adularia-b2.jpg


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rocknroll




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PostPosted: Jun 22, 2018 05:29    Post subject: Re: Identifying adularia  

Pete Richards wrote:
If your specimens have well-formed crystals, there should be no problem distinguishing quartz from adularia. Look them both up on Mindat and look carefully at the shapes of the crystals. Also pay attention to cleavage characteristics.

Hi Pete,

Unfortunately both are too fine to even distinguish individual crystals with the eye!

Thanks though
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rocknroll




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PostPosted: Jun 22, 2018 05:31    Post subject: Re: Identifying adularia  

kushmeja wrote:
I agree with Pete, that if there are discernible crystals, that you should easily be able to tell the difference between the two based on appearance of the crystal structures alone.

Also, a simple hardness test should allow you to tell quartz from andularia, since quartz is harder than feldpar.


I know the average feldspar is 6 on the Mohs scale, but some can be 7 making it more difficult to discriminate.
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rocknroll




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PostPosted: Jun 22, 2018 05:33    Post subject: Re: Identifying adularia  

Jesse Fisher wrote:
Adularia is a varietal name for orthoclase that has a simple prismatic habit. It is commonly found in alpine-type metamorphic rocks. If the material is fine-grained and/or does not show the adularia habit, it should be called orthocalse, or more simply, potassium feldspar (K-spar).

The staining technique that you mention is useful for differentiating k-spar from plagiocalse feldspars, but to my experience, is usually done with petrographic thin sections, and not hand specimen. If you do not have access to thin section making equipment and a petrographic microscope, x-ray diffraction is an easy way to confirm the presence of orthoclase. I believe there is at least one fellow offering this service to collectors, who advertises on Mindat.


Thanks for the info.

We use the term adularia in economic geology literature - referring to a certain pH of fluids. But yes it's generally thought to be a low temperature sanidine.

I know that K-spar is present from XRD, but I'd actually like to identify it in hand specimen.
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Pete Richards
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PostPosted: Jun 22, 2018 08:29    Post subject: Re: Identifying adularia  

If this is a typical rock with intergrown grains, instead of euhedral crystals, the quartz will probably appear grey and translucent and glassy while the adularia will appear whiter and more opaque. Under a binocular microscope, you may be able to detect cleavage in the adularia and observe the conchoidal fracture and lack of cleavage in the quartz.

This assumes these are the only two minerals that you want to tell apart.

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Kevin Schofield




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PostPosted: Jun 22, 2018 09:26    Post subject: Re: Identifying adularia  

rocknroll wrote:
Pete Richards wrote:
If your specimens have well-formed crystals, there should be no problem distinguishing quartz from adularia. Look them both up on Mindat and look carefully at the shapes of the crystals. Also pay attention to cleavage characteristics.


Hi Pete,

Unfortunately both are too fine to even distinguish individual crystals with the eye!

Thanks though


This being the case, I suspect your way forward is petrographic. Quartz and feldspar are easily distinguished in thin section. I assume you do not have the kit to do that, but as you are in the UK, you might look up a company called Kemet on the web. Your local university will probably allow you access to a petrographic microscope.

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