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Tremolite-actinolite skarn with diverse crystals
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Kara




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PostPosted: Aug 16, 2018 07:52    Post subject: Tremolite-actinolite skarn with diverse crystals  

I have a skarn boulder in my garden, which I think you might like to see for there are lots of clear mineral crystals.

I have been told it is an actinolite-tremolite skarn with feldspar crystals and quartz; the analysis being made from photos I have sent. I have also found some other minerals in it, at least possible calcite and something that looks like a banded quartz, but has a weird crystal structure. Also I am wondering if the large crystals are pseudomorphs of some kind, instead of feldspar, for there are green crystals inside them also. Please help me and tell me if you can get more information out of these pictures.

Thank you in advance! Kara

1) the first set of pictures: the tremolite skarn surface and the brown crystal vein



1.jpg
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skarn rock with my pet miniature goat for scale
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1.jpg



1a.jpg
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amphibole mass with veins of large (feldspar?) crystals
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1a.jpg



kide4.JPG
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is this eroded feldspar or a pseudomorph after something?
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pinta1.jpg
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pinta.JPG
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pinta.JPG



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tikut1.JPG
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tikut1.JPG


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Kara




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PostPosted: Aug 16, 2018 08:00    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

2) This is the basic mass of the rock: tiny needle-like amphiboles.


suhru4.jpg
 Description:
tremolite and actinolite, a small piece of the scarn surface (it is eroded and brown, but the real colour is green inside)
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suhru4.jpg



suhru3.jpg
 Description:
there are also bluish needle-like crystals
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suhru3.jpg



suhru1.jpg
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grey needles
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suhru1.jpg



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suhru2.jpg


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Kara




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PostPosted: Aug 16, 2018 08:09    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

3) and this is the funny quartz-looking crystal with a peculiar shape. Pictures taken few years back and yesterday, with some bruises. Is it quartz?

4) The white picture is possible calcite, for vinegar makes fizz and bubbles on it.

5) and the last picture shows some green crystals and some brown ones, no idea of what they are.

Thank you, and apologies for the huge amount of pictures. This rock is so diverse it is very hard to choose the best picture to show the structures.



topsu2.jpg
 Description:
what is this?
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topsu2.jpg



topsu.jpg
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topsu.jpg



topsu1.JPG
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topsu1.JPG



valkoinen1.jpg
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what is this?
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valkoinen1.jpg



pinta2.JPG
 Description:
small green crystals on the top of the picture and bigger brown crystals at the bottom: what can these be?
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pinta2.JPG


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Kevin Schofield




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PostPosted: Aug 16, 2018 08:32    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

Well, I don't know about the minerals, but it's definitely a goat...
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Bob Carnein




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PostPosted: Aug 16, 2018 09:46    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

Hi, Kara, Amphiboles and pyroxenes are notoriously difficult to identify, especially from photographs. So, it isn't possible to do much more than guess (maybe tremolite-actinolite, as you suggest).

To me, the first several (kide) photos look like a member of the scapolite or pyroxene series, though corroded microcline is possible. Punta 2 appears to be stained quartz; valkoinen 1 looks like calcite.
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Pete Richards
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PostPosted: Aug 16, 2018 10:11    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

I agree with Bob about the difficulty of identifying minerals like these from photographs. I also agree about the identification of calcite. Pinta2 looks to me like an iron stained orthoclase (the brown crystals), and Topsu also appears to be a feldspar, not quartz.
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Susan Robinson




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PostPosted: Aug 16, 2018 12:07    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

Was the boulder originally on your property, and are there any similar-looking outcrops of the same type of rock nearby? A locality would help a lot in providing more info.
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PostPosted: Aug 16, 2018 13:25    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

Thank you all very much! You are very kind to educate me.

The boulder is on my property: it was in the pasture, rose up to the surface when a tractor was ditching the field. Haven't found any other similar rock yet, but the soil is very deep in my field so there might be. I live in Ostrobothnia, Finland, and I have studied the basic geological maps of the area. There are many mentions of skarn rocks all over, but I haven't found any detailed information of their composition.

Actually I am a little afraid of the boulder, for someone told me there might be asbestos in it. The boulder erodes very fast, it changes and diminishes every year. I have been thinking of sinking it back to the soil because I am not sure if the dust of tiny crystals it produces, is dangerous if inhaled. Do you know better?

Pete: I wasn't aware there can be banded see-through feldspars, wow! Is there a name for a feldspar like that? I named it "Topsu" which is Finnish slang for topaz, for someone suggested it could be one. Feldspar is quite nice too, so the name shall be "Feldsu" then :).



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Yes I'm a goat :)
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20160806_120732.jpg


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Justin Hickok




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PostPosted: Aug 16, 2018 18:27    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

That's crazy. Not the goat but the rock. Lol.
Looks like it holds a ton of crystals. Man.
You have some really cool stuff Kara. Its like you live in a mineral wonderland.
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PostPosted: Aug 16, 2018 19:50    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

I agree, a great rock, and lots yet to be learned. Kara is asking a lot of good questions. I was hoping someone would pick up on her concern about possible asbestos risks. I know this question comes up frequently from new inquirers, and it would be good for someone with experience on both the rock type and asbestos to comment. My personal reaction is that there is very nominal risk, if any, but some focused comments would, I'm sure, be appreciated.
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PostPosted: Aug 16, 2018 19:55    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

Kara wrote:
Thank you all very much! You are very kind to educate me. [snip]

Pete: I wasn't aware there can be banded see-through feldspars, wow! Is there a name for a feldspar like that? I named it "Topsu" which is Finnish slang for topaz, for someone suggested it could be one. Feldspar is quite nice too, so the name shall be "Feldsu" then :).


Kara, I am at the edge of my expertise here, or maybe beyond, but feldspars are minerals composed of aluminum, silicon, oxygen, together with a mix of the elements sodium, calcium, and potassium. At low temperatures, the potassium feldspars and the sodium/potassium feldspars are two separate minerals, but at high temperatures they can coexist in the same crystal. As the crystal cools, the two minerals stable at lower temperatures separate, forming bands. This is the texture I thought your "Topsu" displayed.

The texture is called perthite if the major component is the potassium feldspar, or antiperthite if the sodium-calcium feldspar (usually sodium) is the major component. If you do a web search for perthite you will certainly see textures that are similar to your crystal. The Wikipedia article, while short, appears correct to me.

I hope this helps more than it confuses!

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PostPosted: Aug 16, 2018 20:27    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

Hi, Kara,

There are several minerals that occur in a fibrous habit and that are collectively called "asbestos". As far as I know, crocidolite (which comes from South Africa) has been more or less conclusively associated with mesothelioma (cancer of the peritoneum and other tissues in the abdominal cavity). In the US, scaring people about mesothelioma seems to be a big business (mostly among attorneys), though few Americans have been exposed to crocidolite. It's mainly found in people who blew asbestos insulation into confined spaces (especially ship workers).

Other kinds of asbestos can cause "asbestosis"--a lung disease--mainly from breathing dust. Unless you are regularly exposed to asbestos dust, I doubt that you will need to bury the rock; in fact, disturbing it may not be a great idea. BTW, if there's one piece on your property, there is probably more. I wouldn't ride a trail bike or ATV regularly over an area underlain by asbestos, but, otherwise, I agree with an earlier writer who said you probably have minimal risk.
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PostPosted: Aug 16, 2018 21:53    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

Being a retired MD pathologist with some asbestos mineral toxicity experience, I have previously posted a complete discussion of this problem several times; at least twice on Mindat and maybe previously on this website (I don't remember). Anyway again here goes.

In the 1950s it was noted that certain groups of workers exposed, over a long period of time, to aerosolized dust of certain types and fiber sizes of asbestos during work had a statistically significant increase in several types of lung diseases. The diseases included a fibrous thickening of lung tissue and mesothelial lung lining tissue. This was called asbestosis. The lung and pleura couldn't expand properly and these folks got a terminal chronic disease with increasing shortness of breath.
They also had a statistically increased number of lung cancer cases.
Of most interest, however, was the strong statistical association with a rare cancer of the lung lining.....the mesothelium......so they had hi numbers of malignant mesotheliomas. This was a cancer, but a sarcoma and not a carcinoma as it involved the mesothelium and not the lung tissue per se, an epithelium. Any way if the workers smoked, the disease rates for all types was further increased. In addition there was an increase in abdominal mesotheliomas not involving the lungs.

Those folks with hi disease rates included ship yard workers who sprayed asbestos containing fire retardant insulation while building ships. Those folks living down wind from the asbestos mining quarries had less statistically significant increases in the diseases.

As I mentioned, only certain types and sizes of the asbestos fibers caused the majority of disease. Fibers were easily visible under the microscope, in the tissue, with appropriate lighting, using a polarizing scope, as they were refractile in tissue samples from workers who were sick or died from disease.

The important points here are that dusty air with poor ventilation and no filter masks with long exposure to aerosolized fibers of the offending type needs to be the conditions. Only danger of carefully handling collector type asbestos minerals is getting a fiber into the skin like a splinter or dropping a heavy specimen onto your foot.....NO LUNG DISEASE comes from routine careful handling or very brief exposures of other types!

I hope that my primer on the subject answers the questions. BOB
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PostPosted: Aug 17, 2018 05:13    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

I very much agree with Bob Harman about the absence of a cancer risk so you do not have to bury this wonderful rock. I am somewhat in disagreement with some of the statements made about the major composition of your rock which is, to my eye, just as you suspected - actinolite-tremolite, both the large well-formed crystals and the interlocking fibrous looking crystals in the darker sample which appears to have been broken off of the large rock. The large crystals look very much like tremolite that has replaced diopside crystals, examples of which I have personally collected not far from where I live, some of which are shown in the photographs posted here. There are to be other minerals expected in a skarn but it is very difficult to suggest what they might be from photographs, especially when they have been weathered.


Diopside - Maryland 27-6-3 (fluorescent).JPG
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Diopside - Maryland 27-6-3 (fluorescent).JPG



IMG_0927.JPG
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IMG_0927.JPG



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PostPosted: Aug 17, 2018 07:16    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

I really appreciate your help and cannot thank you enough. It is a privilege and feels very special to get guidance from true masters. I am very, very, very grateful. This is so interesting my heart pounds crazy.
Justin, I really feel like Alice in wonderland now.

Asbestos:
Bob and Bob and Jim: Very interesting and eye-opening information to read, thank you for giving me such a detailed explanation.

Big crystals:
John: the large brown crystals do indeed have green crystals inside them, and the overall structure is like a honeycomb with open spaces. Here picture no (2a) is showing it: it is a smaller crystal I cracked in half. Also pictures (2) and (2aa) from bigger crystals are showing the greens.
(Edit: hey I just looked at the Mindat page of tremolite and there was a photo of pseudomorph after diopside, that really looked a bit the same.)

The banded crystal perthite:
Pete: It was super interesting to learn how the bands form. I have found some similar-looking chunks with a little wider banding. I have been thinking these are quartz, but can they also be feldspar then? Pictures (0) and (0a).

Actinolite-Tremolite?:
The last picture (4a) shows some delicate star-shaped crystal clusters.

Other minerals in the boulder:
Yes there are some more, I will post photos of them later if you like.



2a.jpg
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Brown crystal cracked in half
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2a.jpg



2.jpg
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2.jpg



2aa.jpg
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2aa.jpg



0.jpg
 Description:
perthite banding?
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0.jpg



0a.jpg
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perthite banding?
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0a.jpg



4a.jpg
 Description:
star-shaped structures
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4a.jpg


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PostPosted: Aug 17, 2018 09:30    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

Kara wrote:
I really appreciate your help and cannot thank you enough. It is a privilege and feels very special to get guidance from true masters. I am very, very, very grateful.

[snip]

The banded crystal perthite:
Pete: It was super interesting to learn how the bands form. I have found some similar-looking chunks with a little wider banding. I have been thinking these are quartz, but can they also be feldspar then? Pictures (0) and (0a).


In this case I think the mineral is more likely quartz. In a perthite, all of the bands should be parallel, though there can sometimes be two sets of bands with different orientations. In this specimen, the bands are not all straight, nor are they parallel. Feldspar has good cleavage, so there should be some broken surfaces that are flat. I don't see indications of such cleavage surfaces on this specimen either.

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PostPosted: Aug 17, 2018 09:35    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

That is a VERY interesting mineral boulder you have there!...with some nicely developed crystals. I suspect if you were to carefully go inside of it with rock hammer and chisels you would likely find even better ones - that have not had as much exposure to abrasion and water, etc. If you are new to things like that, make sure you use eye protection from flying bits of rock and read up on some techniques least likely to destroy what you most want not to destroy. Some of the Sinkankas books have interesting chapters for the beginner on such things...if one can find one there in Suomi - perhaps at a library - or ask a mineral hunter or ask here. I'd also guess that if there was that one, there are likely many others on your land under the soil....!
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PostPosted: Aug 17, 2018 11:00    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

Thank you Pete, and Peter. Don't know if I have the guts to go and hammer it, because of the needle-like greys and greens that dart all over the place.

There is the other wing of the boulder too, very different. There is a big grayish bluish vein going down (I think some amphibole too) (pics 6, 6b, 6c), tiny burgundy crystals (pic 7) and something that looks like gold, perhaps eroded mica or something (pics 5, 5a) . Also there are some eroded long flat crystals that look kind of like spodumen. These are older photos and not so very good quality. I think the layer with the burgundies has already eroded to bits, but there might be little bit left of those "gold" veins. This erodes very fast and exposes new holes and small caves after almost every winter.

Here some pictures of the other side.



6c.JPG
 Description:
the bottom of the other side, old picture
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6c.JPG



6b.JPG
 Description:
pale bluish gray vein
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6b.JPG



6.JPG
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6.JPG



5.jpg
 Description:
don't know
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5.jpg



5a.JPG
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5a.JPG



7.JPG
 Description:
burgundy/purple shiny crystals - are they garnets?
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7.JPG


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PostPosted: Aug 17, 2018 12:53    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

An awful lot of different crystals. The photo of the purple one is not clear enough to try to identify. Shape and hardness would determine if it were garnet...but could be other things too.Try a photo with better focus and showing as much of the shape of the purple crystal as possible - or a few of them if there are more than one....

Are there any rock outcrops near your property with similar mineralization? The more interesting crystals, and the larger ones, seem to be in or near the cavities in the rock - this is not surprising. Looking deeper inside those cavities with a light and even a small mirror, you might find some very interesting crystals.....or the same types, but less weathered. Some of the XX [crystals] in photo 1a look quite large and well-formed! Better will almost surely be found below them [inside the rock].

To really get an idea of what is there would take doing a little hammering with a big chisel of at least a corner that is not too weathered and with some seemingly interesting crystals.....but it is yours and if you don't want to 'hurt' it or alter it this is up to you. I'd certainly long ago have looked inside if I found one like that. If you really don't want to hurt the rock's feelings, you might try cleaning some of the XX with high-pressure water spray from a garden hose with a small hole in a cap screwed over the end - to clean off the accumulated dirt, moss, lichen, etc. It likely will not hurt any of the XX and you can slowly turn up the pressure to see if some are more fragile than others.

If you have a local university with a geology department, you might send them the photos...they might be interested and/or might know about minerals found in that area in detail. Below a lot of your soil, I would imagine lie many more XX than you have in that one rock! Lucky you! If you care to mention the general area of Finland you are in, I have an old German guide to some interesting mineral collecting areas in Finland and can look in the general area. Or you and the goat can keep it your secret ;-)
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PostPosted: Aug 17, 2018 23:45    Post subject: Re: Tremolite-actinolite skarn with diverse crystals  

Peter: Thank you for your advice. The boulder isn't mossy and covered with clay anymore: the last pictures I sent were old. I did clean the boulder a few years ago with a high pressure washer, but don't dare to do it again for I don't want the darting needle-like minerals and mineral dust all over me. For the same reason, I don't want to hammer it, but can ask someone with experience and equipments, to do it.

As I wrote earlier, I think the layer with the burgundies has already eroded to bits. The purple crystals are, I think, long gone now and fallen off to the soil beneath. This is the only pic I have of them. I can go and try to find if there are more I haven't seen yet.

The idea of a small mirror is great. The cavities are webbed: when I pour water inside one, after some time it pours out from other cavities. With lot of ants.. they have found the holes and came and go all the time. So, I might have some biological formic acid etching going on inside there.

I haven't found any outcrops like this but there are mentions of found skarn boulders in the Ostrobothnia area. Peter, you are very kind to offer help with the collecting guide, but I realized I can contact the Geological Survey of Finland to ask for more data of my area and maybe ask if a geologist had the time to came and see the rock when passing by.

Here the worst pictures ever; more funny shaped things lurking in the rock.

I thank all of you for your help with this rock, you really got me interested and determined to find out more. Respectfully, Kara



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