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Crystal vein again
  
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Kara




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PostPosted: Sep 02, 2018 23:47    Post subject: Crystal vein again  

Black and colourless crystals in grey veins on quartz.

Found this boulder from a forest nearby, but didn't have any sample collecting equipment with me. So just pictures. I know they cannot be identified like this so I just want to show you a bunch of tiny wild beauties. There are black and colourless (or slightly blueish/greenish) smooth crystals that don't look like tourmaline for there are no stripes. A beautiful rock I think. Finland.



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Kara




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PostPosted: Sep 03, 2018 00:07    Post subject: Re: Crystal vein again  

(ps. there are lots of black tourmalines in these forests, but all I have found are in pegmatites like these)


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Peter Lemkin




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PostPosted: Sep 03, 2018 00:38    Post subject: Re: crystal vein again  

Kara, you really seem to be in a pegmatite area! Lucky you! Pegmatites can be VERY interesting and can have many interesting crystals that are sometimes well-formed and large. They often, but not always, are in 'pockets' within the pegmatite. The black tourmalines can often be used to point to the pockets, and also often mark the outer limit of the pegmatite. There is a lot to learn about pegmatites and how to 'read' them - too long and complex to list here. I suggest you find some book chapters or articles on them at a level you can understand. The best book on the subject I know of is a special publication by the Canadian Mineralogical Society - but not a book for novices. These loose pieces of pegmatite in you photos must have broken off from an intact one in place in rock - and that would be uphill, or upstream - and you might try to find that pegmatite[s]. They may be hidden under dirt, but also may not be. However, there may well be interesting things in what has broken off too.....

If you look on the internet or in not too advanced geology or mineralogy books you will find information on pegmatites. Two [not very easy articles, but informative] I found on the internet by one of the experts can be found and downloaded here:

http://www.pitt.edu/~cejones/GeoImages/2IgneousRocks/IgneousTextures/5Pegmatitic.html

https://www.researchgate.net/publication/238667995_The_classification_of_granitic_pegmatites_revisited

http://www.cvmineralclub.org/MAIN/Pages/Members%20Articles/Noyes/Gem-Bearing-Pegmatites-A-Review.pdf
(links normalized by FMF)

...but you can find many others with more basic information and photos, etc.
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Kara




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PostPosted: Sep 03, 2018 03:06    Post subject: Re: crystal vein again  

Thank you Peter very much, again! I will definitely study the links you gave. And yes we have different pegmatites here: erratic blocks and rounded rocks in glasiofluvial deposits and pegmatite outcrops and veins too, very beautiful. I have found nice apatite crystals and other yet unidentified crystals in them. Pegmatites are my favourite.

If you like to see pictures, here some beautiful esker pegmatites.



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spodumen pegmatite
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Peter Lemkin




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PostPosted: Sep 03, 2018 03:37    Post subject: Re: crystal vein again  

Some of those look long water-worn....are you near a river? If so, follow upstream until you find the pegmatite source [or the stones with pegmatites stop [you have gone too far]. Others seem to be on land - follow those uphill until your find the pegmatite source or stones with pegmatites stop. Somewhere not too far from you must be some massive pegmatites still in place which may contain some interesting XX. Not all pegmatites have cavities with XX inside them and what XX there are are frozen in the rock like fruit in gelatin. Even these can be gotten out intact if you know how....or just admired and photographed if you prefer. The Finnish Geological Survey likely knows generally or specifically where the pegmatites in your area are and I would contact them and ask. Good geological maps of your area may also help if you learn how to read them. All rocks contain grains or crystals of minerals - but pegmatites contain very large crystals often and also contain some rare and exotic elements that crystallized and are of mineralogical and aesthetic interest. You seem quite lucky to live where you do and won't have to travel far to find many interesting things, I think.
The more you learn about pegmatites and how they form - as well as how to look for them and the features within them, the more you will find and appreciate what you find.
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Kara




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PostPosted: Sep 03, 2018 04:25    Post subject: Re: crystal vein again  

The whole area is mostly former seafloor brought to surface by post-glacial rebound and the accumulation of alluvial sediment. We have post-glacial rebound raised beaches, glacial river deposits and glacial erratics all around the inlands here. Most of these pics are taken in esker areas, of esker deposits, which are ridges of stratified gravel formed within ice-walled tunnels by streams which flowed within and under glaciers. So there's no telling how far the boulders or even smaller rounded rocks have travelled.
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Pete Richards
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PostPosted: Sep 03, 2018 08:25    Post subject: Re: Crystal vein again  

You have some amazing rocks around you, Kara! The starburst of black tourmaline in orange feldspar, white feldspar, and quartz (I think) is striking!

The one you started this post with has the brownish, kind of twisted material on it on one side. This looks like a mica schist - a metamorphic rock - and I would guess that the long dark brown crystals might well be staurolite.

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Peter Lemkin




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PostPosted: Sep 03, 2018 08:33    Post subject: Re: Crystal vein again  

Aha.....makes it harder, but maybe not impossible. You have been showing an awful lot of large crystalline material - much [not all] of it definitely pegmatite materials. Pegmatites are not so common, although in some areas they can be extensive and I'd have to imagine that if this was moved by a glacier, that glacier moved over some large pegmatites - which may well still be in place. Even that piece that [if I remember correctly] came from deep under soil in on your land looks like it might be similar - and with all that soil on it, was likely deposited there a long time ago unless some sea or other water body [river, etc.] is around to cover up some of the rocks with soil. Those well-rounded ones you showed above were long being polished by rubbing against ice or other rocks - some of the others hardly look like they have traveled very far from the pegmatite - as the rock seems 'fresh' and not abraded much or at all to my eye. The entire Scandinavian shield is uplifting still [but very slowly on human terms], but is your area doing so at a more rapid rate - or are glaciers not long ago there melting away due to climate change? Question - about what % of rocks in that area show signs of being pegmatites? Also, are you showing some rocks at the sea shore? You should ask a group of geology graduate students to explore your area...it seems to more interesting that the average. A lot of those large black crystals almost certainly are tourmaline. Those tourmaline that are far from the core of a pegmatite tend to be friable [easily fall apart/fracture]....those nearer the core can be very hard and even gemmy and in such an area there well might be some rarer and interesting pegmatite minerals. Now I'm wondering why I spent so much time collecting in Norway and Sweden and have ignored Finland so far..... ;;-) Apua!
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Kara




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PostPosted: Sep 03, 2018 09:22    Post subject: Re: Crystal vein again  

Thank you Pete!

Peter actually yes, the Bothnian Bay area is uplifting faster (nearly 1 cm per year) than in other areas for the ice shield was thickest and stayed long here, with a huge freshwater Ancylus lake on top of big area of Finland. This is a really fast geological change rate. The smallest uplift is in the Southeastern Finland with less than 3 mm per year. And for example, there's no visible uplift in St Petersburg anymore.

We have lots of giant boulder fields of ancient shoreline formations here inlands. If you are interested in seeing one, here is a beautiful short video of one of my favourites: The "Töppösen luolikot". It is saed, that "Strong wave action has even crushed the smaller stones of the boulder field. The shore forces were so strong that hardly any stones smaller than 20 cm (8”) are left, and even the larger ones, several meters in diameter, have been rounded. Over the years the boulder field, originally more than 750 hectares (1850 acres) in size, has been partly covered by bogs while patches of forest have grown up in the highest spots. This has resulted in a unique patchwork landscape."

Here: https://www.youtube.com/watch?v=btCsBAISsrU

( or if the link doesn't work, go to Youtube and make a search for Töppösen luolikko. )

If and when you visit Finland some day, I can take you there.

EDIT: No, there are no rocks in these photos from the sea shore, they are all almost 100 km inlands in esker areas. There are lots of perfectly rounded rocks in the old glasiofluvial deposits. And, I have no idea of the pegmatite % you asked for, for I really am just a novice in this rock hobby. I have only seen maybe 0,1% of the rock types here.. :)
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Bob Carnein




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PostPosted: Sep 03, 2018 12:13    Post subject: Re: Crystal vein again  

The black elongate crystals in your first 3 photos look, to me, like tourmaline (schorl). If you can get an "end view" of a few of them, they should have a somewhat rounded triangular cross section.
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sfpa sunstone




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PostPosted: Sep 04, 2018 20:38    Post subject: Re: Crystal vein again  

Hello I just joined the forum , my name is Kevin . Those are some weathered rocks . Very cool , the small river stones and the one photo with tiny tourmaline / schist ? on it was very nice . The river stones with the inclusions could make a great hearth or some decoritive accent in a cabin / rustic home . I look forward to discovery . K
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Peter Lemkin




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PostPosted: Sep 04, 2018 23:42    Post subject: Re: Crystal vein again  

sfpa sunstone wrote:
Hello I just joined the forum , my name is Kevin . Those are some weathered rocks . Very cool , the small river stones and the one photo with tiny tourmaline / schist ? on it was very nice . The river stones with the inclusions could make a great hearth or some decoritive accent in a cabin / rustic home . I look forward to discovery . K


As stated above, the crystals in the schist for several reasons are likely staurolite. Tourmaline is rarely to never found in schist, are black rather than brown and there are other reasons.
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Bob Carnein




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PostPosted: Sep 05, 2018 09:21    Post subject: Re: Crystal vein again  

Actually, Peter, I've found tourmaline in mica schist in various parts of the Appalachians--it isn't rare at all. (confirmed in thin sections and with immersion oils). My experience is that it tends to occur where pegmatites are nearby, but I also seem to remember learning that it is typical in schists derived from marine sediments. Kara's crystals look black to me, but, of course, tourmaline can be brown also.
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Kara




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PostPosted: Sep 05, 2018 10:44    Post subject: Re: Crystal vein again  

Thank you Bob. Yes the crystals are jet black, smooth and different in shape and surface from the staurolites I have collected here. If they appear brown in the pictures, it is because of the light or surface dirt/algae.

I am still wondering about the bright colourless/greenish crystals among the black ones. Here a zoom picture where you can see some of them in the middle. There are no better pictures I am sorry. I will visit the rock again later.



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Bob Carnein




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PostPosted: Sep 05, 2018 15:42    Post subject: Re: Crystal vein again  

I'm not sure I see what you are asking about. There definitely are greenish-brown crystals, clearly visible especially when you blow the image up.

Are the black crystals striated? Once again, if they are tourmaline (and that's definitely an "if" because photo IDs are always iffy), they should have rounded triangular cross sections.
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Kara




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PostPosted: Sep 05, 2018 19:27    Post subject: Re: Crystal vein again  

I don't know about the cross section shape - I only have these these pictures for I didn't take any pieces with me. I remember the black ones being glass smooth, long and narrow and with no stripes. Not looking like striated, I didn't think they were tourmalines. But they didn't look like staurolites either. The shorter and thicker greenish ones in the middle looked more uneven in shape. ,
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Kara




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PostPosted: Sep 06, 2018 00:25    Post subject: Re: Crystal vein again  

I understand they cannot be identified from the pictures. I thank you all very much for helping me and giving the alternatives what they can be. I will find the rock again and take a good loupe plus better camera with me. It will be easier to study them for now I know what identification features to seek.

Thank you! Kara



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black tourmaline
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dark staurolite
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poss. staurolite / tourmaline
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Kara




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PostPosted: Sep 08, 2018 01:27    Post subject: Re: Crystal vein again  

I just found this fine photo of tourmaline micaschist, presented by prcantos. I think it looks much the same.

https://www.mineral-forum.com/message-board/download.php?id=37435
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