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Purple mineral in greenstone
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Kara




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PostPosted: Jul 23, 2018 06:00    Post subject: Purple mineral in greenstone  

Please can you help me identify this mystery purple mineral I found from Finland.

Other minerals included in these rocks are, as far as I know (fluffy newbie..) , chlorite, serpentine, epidote, some amphiboles. Dropped some pieces to vinegar acid bath and the white mineral dissolved, so it might be calcite.

I have absolutely no idea of this purplish mineral, and don't have any lab equipment to test it. Is it possible to identify it from these pictures?


First set of pictures: samples with no acid treatment, the colour is a bit off (too bluish)

Thank You in advance! - Kara, Finland



5.JPG
 Mineral: don't know
 Dimensions: different sizes, hand in comparison
 Description:
 Viewed:  1150 Time(s)

5.JPG



7.JPG
 Mineral: don't know
 Dimensions: different sizes, hand in comparison
 Description:
 Viewed:  1148 Time(s)

7.JPG



8.JPG
 Mineral: don't know
 Dimensions: different sizes, hand in comparison
 Description:
 Viewed:  1150 Time(s)

8.JPG



9.JPG
 Mineral: don't know
 Dimensions: different sizes, hand in comparison
 Description:
 Viewed:  1149 Time(s)

9.JPG



9b.JPG
 Mineral: don't know
 Dimensions: different sizes, hand in comparison
 Description:
 Viewed:  1152 Time(s)

9b.JPG


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Kara




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PostPosted: Jul 23, 2018 06:14    Post subject: Re: Purple mineral in greenstone  

And here are some sharper pictures of pieces after vinegar bath. Loose and sharp structures. Pinkish rosy purple colour.


a.JPG
 Mineral: don't know
 Dimensions: different sizes 5-8 cm
 Description:
 Viewed:  1139 Time(s)

a.JPG



aa.JPG
 Mineral: don't know
 Dimensions: different sizes 5-8 cm
 Description:
 Viewed:  1137 Time(s)

aa.JPG



aaa.JPG
 Mineral: don't know
 Dimensions: different sizes 5-8 cm
 Description:
 Viewed:  1138 Time(s)

aaa.JPG



aaaa.JPG
 Mineral: don't know
 Dimensions: different sizes 5-8 cm
 Description:
 Viewed:  1136 Time(s)

aaaa.JPG



IMG_7158-001.JPG
 Mineral: don't know
 Dimensions: different sizes 5-8 cm
 Description:
 Viewed:  1131 Time(s)

IMG_7158-001.JPG


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Kara




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PostPosted: Jul 28, 2018 05:40    Post subject: Re: Purple mineral in greenstone  

More information, sorry for being late with these:

- hardness 3, both the green matrix and the purple mineral in question. Copper coin makes a scratch to both. But, I don't know is it due to that the purple area consists of a higgledy-piggledy mess of tiny sharp flat crystals - don't know if the layered structure just collapses/crumbles/pulverizes under pressure. Oh, it's so hard to describe stuff in foreing language :p (edit: when soaking in the vinegar bath, lots of tiny sharp purple particles fell to the bottom when the white mineral surrounding them, slowly dissolved.

- white or colourless streak (on a white fuse)

- I don't dare to say anything of the luster or form for I am a beginner in this, it would go wrong. I hope you can see something from the pictures.

I hope you can somehow help me. K
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Riccardo Modanesi




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PostPosted: Jul 28, 2018 07:26    Post subject: Re: Purple mineral in greenstone  

Hi Kara!
Have you ever tried to make it react to chloridric acid? Does it fizz?
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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Kara




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PostPosted: Jul 28, 2018 07:32    Post subject: Re: Purple mineral in greenstone  

Hey Riccardo, thank you! I only have vinegar and citric acid at home. Soaked some of them in vinegar bath for a couple of days and most of the white mineral around them dissolved with a fizz. But, the purple mineral didn't, lots of tiny purple "needles" or "crumbs" just fell unharmed to the bottom of the glass.

EDIT: I will find me some better acid to test with.
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Bob Carnein




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PostPosted: Jul 28, 2018 10:02    Post subject: Re: Purple mineral in greenstone  

When testing hardness with a coin, always try scratching the coin with the mineral, rather than the other way around. If you put pressure on the coin, you may crush the mineral, rather than scratching it If it scratches the coin, try scratching a piece of glass with the mineral and tell us the result. Can you describe the shape of the "purple" crystals?
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Kevin Schofield




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PostPosted: Jul 28, 2018 10:06    Post subject: Re: Purple mineral in greenstone  

Kara wrote:
More information, sorry for being late with these:

- hardness 3, both the green matrix and the purple mineral in question. Copper coin makes a scratch to both. But, I don't know is it due to that the purple area consists of a higgledy-piggledy mess of tiny sharp flat crystals - don't know if the layered structure just collapses/crumbles/pulverizes under pressure. Oh, it's so hard to describe stuff in foreing language :p (edit: when soaking in the vinegar bath, lots of tiny sharp purple particles fell to the bottom when the white mineral surrounding them, slowly dissolved.

- white or colourless streak (on a white fuse)

- I don't dare to say anything of the luster or form for I am a beginner in this, it would go wrong. I hope you can see something from the pictures.

I hope you can somehow help me. K


Hi Kara,

Firstly, thanks very much for providing the information on your basic tests, and some good "before and after" pictures. In terms of identification, it's probably best to start at the rock scale and then move to the constituent minerals. SInce you live in Finland, it's a pretty fair bet that your rock is very old and has been messed about quite a bit over the past half-billion to one-and-a-half billion years and that it has been at least somewhat metamorphosed That, plus the colour of the rock (grey-green, green and purple, with a smattering of white crystalline material) suggests to me that you are already pretty close to identifying what is going on in your second paragraph, where you identify serpentine, chlorite and amphiboles as present in the rocks. That suggests then that you are dealing with a low-grade metamorphic rock we could call serpentinite. Your good description of the properties of your purple mineral (soft, tiny sharp flat crystals) suggests a phyllosilicate, so given the rock association and colour, I think your mineral may be a chromian antigorite (look up Antigorite on Mindat, and you'll see something a little similar to what you have).

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Kara




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PostPosted: Jul 28, 2018 12:29    Post subject: Re: Purple mineral in greenstone  

Bob Carnein wrote:
When testing hardness with a coin, always try scratching the coin with the mineral, rather than the other way around. If you put pressure on the coin, you may crush the mineral, rather than scratching it


Oh, thank you , I have done it all wrong then! I have pushed the coin against the rock like a madman. This was a good advice.

And for your question of the structure, I cannot describe any better than tiny sharp flat crystals pointing to every direction (after the white mineral is gone). I am sorry :) I think flat is the best description.

here one more pic, colour is too pale



IMG_7348.JPG
 Mineral: maybe antigorite
 Dimensions: 4 cm
 Description:
 Viewed:  843 Time(s)

IMG_7348.JPG


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Kara




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PostPosted: Jul 28, 2018 12:56    Post subject: Re: Purple mineral in greenstone  

Kevin Schofield wrote:
..rock we could call serpentinite. Your good description of the properties of your purple mineral (soft, tiny sharp flat crystals) suggests a phyllosilicate, so given the rock association and colour, I think your mineral may be a chromian antigorite (look up Antigorite on Mindat, and you'll see something a little similar to what you have).


Thank You for the good description! I looked at Mindat and the chrome antigorite really has the same colour. Most of the pictures had different structure with long plates, but if they can be tiny and short like in these rocks, it really can be it! I browsed Google for "serpentinite purple.." and found also something called Stichtite that also looks a bit the same?

Here another picture of another rock where the purple is setted differently. Thank you very much for your help!



IMG_7339.JPG
 Mineral: maybe cromian antigorite
 Dimensions: hand in comparison
 Description:
 Viewed:  833 Time(s)

IMG_7339.JPG


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Bob Carnein




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PostPosted: Jul 28, 2018 16:09    Post subject: Re: Purple mineral in greenstone  

Another possibility is chromian clinochlore, which occurs in Lapland (Kemi mine, Kemi, Lapland).
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Kevin Schofield




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PostPosted: Jul 29, 2018 08:02    Post subject: Re: Purple mineral in greenstone  

Kara wrote:
Kevin Schofield wrote:
..rock we could call serpentinite. Your good description of the properties of your purple mineral (soft, tiny sharp flat crystals) suggests a phyllosilicate, so given the rock association and colour, I think your mineral may be a chromian antigorite (look up Antigorite on Mindat, and you'll see something a little similar to what you have).


Thank You for the good description! I looked at Mindat and the chrome antigorite really has the same colour. Most of the pictures had different structure with long plates, but if they can be tiny and short like in these rocks, it really can be it! I browsed Google for "serpentinite purple.." and found also something called Stichtite that also looks a bit the same?

Here another picture of another rock where the purple is setted differently. Thank you very much for your help!


I believe that you may have hit the nail on the head with stichtite, especially with the association with calcite. Good detective work!

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Kara




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PostPosted: Aug 01, 2018 05:11    Post subject: Re: Purple mineral in greenstone  

Hello again!

I wanted to be sure of this purple mineral and sent a piece of it to a geologist for testing. The results are very interesting.

1) the mineral is fluorescent emitting blue light, but very faintly.

2) the XRF (X-Ray Fluorescence) showed that there is no chrome present in the sample, but lots of calcium

Therefore it cannot be antigorite, clinochlore or stichtite.
The conclusion was, this is FLUORITE.
(most likely, 95% sure).

- The rare columnar structure can be explained by difference in crystallization rate in the opening vein. I have the explanation here in Finnish but it is a bit hard for me to translate it to English properly.

- the weak fluorescence can be explained by iron impurities which can dim the fluorescence.

Have you seen fluorites like this before?



IMG_1341.JPG
 Description:
colours too dull because pic taken with a cell phone camera
 Viewed:  580 Time(s)

IMG_1341.JPG


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Oliver B




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PostPosted: Aug 01, 2018 08:11    Post subject: Re: Purple mineral in greenstone  

the cross section looks a lot like Blue John fluorite, maybe the same growth structure occured in a different locality? Also the fluorescence in many of my samples seemed to lose its intensity if it was found exposed to sunlight for prolonged periods of time. Not sure but those are my thoughts. Tight crystal growth in a compact area and chemical impurities or sunlight destroyed or decayed some organics present that produced the fluorescence.
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Kara




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PostPosted: Aug 01, 2018 08:43    Post subject: Re: Purple mineral in greenstone  

Thank You Oliver!! A million times thank you, super interesting! I am just now madly in love with these rocks and studying everything I can find about Blue Johns. I can call these " Blue Finns" ... 😃
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Oliver B




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PostPosted: Aug 01, 2018 10:30    Post subject: Re: Purple mineral in greenstone  

Blue Finns :D omg haha what a good joke for this morning. I cant confirm my thoughts on these samples as i am only self taught but thats my best take on them!
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Bob Harman




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PostPosted: Aug 01, 2018 10:50    Post subject: Re: Purple mineral in greenstone  

I must say that I am skeptical of your purplish mineral being fluorite. Not knowing anything about Finnish minerals, I just am not sure. One of your earlier pictures shows the mineral with a bit of conchoidal fracture and many of your other pics show, what I consider, to not be consistent with the pattern or even the color of fluorite. So while I am not sure, I remain skeptical.

As to OLIVER's idea of blue john, it is not that. Blue john has a quite specific pattern and appearance. These examples are neither the same colors nor patterns. In addition, classic "blue john" comes from several specific sites in the UK and a similar pattern is found in fluorite from a China locality. Vaguely similar appearing banded fluorite is found in other localities, but those examples are usually not considered classic "blue john". BOB
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Kara




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PostPosted: Aug 01, 2018 11:18    Post subject: Re: Purple mineral in greenstone  

Thank You Bob for the information. It is interesting to hear others thoughts and given possibilities too. The sample I sent was seen by two more colleagues before they named this fluorite. I can of course send a new sample for double checking.

And, the Blue Finn thing was meant to be a joke, by no means I would really give any mineral any names of my own. It is sometimes hard to write one's thoughts in foreign language.

Edit: there's also a possibility to send one sample for Raman Spectroscopy, I think I will do that for I have some other samples too to send there. This is so very interesting!
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Kara




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PostPosted: Aug 01, 2018 13:22    Post subject: Re: Purple mineral in greenstone  

It's me again.. Look what I found browsing the Finnish Geological Survey database called Hakku. This is a fluorite specimen that looks the same-ish, don't you think?

Edit... oh, I can't seem to post any links here. So, if you want to see the picture, take a Google search for: GTK Hakku. There's an english option on the upper right side, take it. Then go to Photos and do a search for " fluoriitti scheeliitti ".
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Jordi Fabre
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PostPosted: Aug 01, 2018 13:41    Post subject: Re: Purple mineral in greenstone  

Kara wrote:
...I can't seem to post any links here...

Please use: Links within the message forum
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Bob Carnein




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PostPosted: Aug 01, 2018 15:16    Post subject: Re: Purple mineral in greenstone  

Kara, you may be right, but I agree with Mr. Harman. These specimens don't look at all like any fluorite I've seen (and that's a lot!). How reliable do you think your analysts are?
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