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Massive graphite?
  
  Index -> FOR BEGINNERS: What is it? Where is it from?
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Kara




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PostPosted: Nov 27, 2018 14:58    Post subject: Massive graphite?  

Hello again. I have trouble identifying this thing. (the long one on front)

Hardness is about 2 or under (can be scratched with a fingernail but have to use pressure) so it fits graphite, but it gives a grey streak instead of black. I read that molybdenite should be very stainy - this is not so stainy, my hands are not so very dirty after handling this. When tickled with a fork and a key and everything harder than nail, it gets deep pale streaks and produces "dust". My verynotscientific report :)

Thank you in advance! Kara

(Edit:: I deleted photo no 3 because I realized I had taken it from the other rock behind)



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John Betts




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PostPosted: Nov 27, 2018 15:16    Post subject: Re: Massive graphite?  

Where was it found?
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Kara




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PostPosted: Nov 27, 2018 15:22    Post subject: Re: Massive graphite?  

From Finland.

Edit: I just found something called graphitic schist from the internet. There is almost similar looking picture in Sandatlas webpages about schist, picture no 2 (graphitic schist from the Urals, Russia). Could it be the answer here, being so soft?
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Bob Carnein




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PostPosted: Nov 27, 2018 16:09    Post subject: Re: Massive graphite?  

This looks like a fine grained schist or phyllite. It could be graphitic, but even a micaceous phyllite will be very soft. Whether any graphite is identifiable really depends on microscopic work (or guesswork). Many black slates and phyllites contain carbon: hence the dark color.

Sorry that sounds like waffling. What I'm saying is that certain identification of any rock, whether metamorphic, igneous, or sedimentary, depends on microscopic thin-section study and, to be really certain, a quantitative count of mineral grains.
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SteveB




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PostPosted: Nov 27, 2018 16:12    Post subject: Re: Massive graphite?  

I’m wondering if it could be something more related to mica. I’ve got some specimens that look similar and because its sort of like compressed mica layers it takes on a rounded look like yours as handling flattens it all down. Sort of like like stroking fur flattens it.I can’t recall off hand what likely minerals I’d narrowed mine down to as i havent completed tests yet. I’m not familiar with graphite specimens so cant say its not. Sheetlike cleavage and a fibrous sheen leads me towards a mica group.

Those specimens are a good healthy size how about doing some water displacement density measurements on them to get yourself another data point. Try to confidently pin down hardness value too then you have two quantifiable numbers to exclude various minerals.

If you know the source location better you could look at mindat to see what minerals have been recorded from that area and then you can investigate those, comparing your test results with values for the other minerals and maybe find a shortlist of close matches that others can help you determine which ones could or could not be your specimens. Also keep in mind mindat etc do not know of every mineral in every location so yours may or may not be known for the region.
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Pete Modreski
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PostPosted: Nov 27, 2018 16:52    Post subject: Re: Massive graphite?  

Looks like you are getting lots of replies, to keep you "in the right ballpark", which you are "already in" with what you've said, Kara.

I was going to say--the trick is, distinguishing pure graphite from a fine-grained, graphitic, mica schist. Since there are all possible variations of proportions, from trace graphite in mica schist, to trace mica mixed with graphite--well, there you have it.

If it's really mostly pure graphite, it will easily leave a black (or dark gray) streak on even soft materials--such as on paper, or your skin. Normal mica schist would not "write" on paper.

You may want to go back to your improvised "microscope", using a hand lens. Look at loose/crushed grains under magnification. Flakes of mica will be transparent; flakes or bits of graphite, completely opaque. See if that helps?
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Kara




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PostPosted: Nov 28, 2018 10:00    Post subject: Re: Massive graphite?  

Thank you very much for help and advice! I studied it again and yes I now think it indeed is a very fine grained graphitic schist/phyllite, because:

a) it writes dull gray on paper and smudges my fingers with sticky but very pale gray. When wiped the gray stays on both on paper and on my finger = graphite?

b) it has also tiny sparkly flakes which fall off from the paper and some of them from the porcelain fuse also, when wiped = mica?

There are both opaque and transparent grains in my "wannabemicroscope", with the smallest grain size.

When rubbed with a porcelain fuse, the rocks soft flaky surface turns into polished "clay-like" spot seen in the pictures. A knife cuts through deep and also I can write letters to the surface with my fingernail and lots of pressure.

I searched for geological information about the area, and graphite is found very close at least in scheelite skarn and in black schist. I also have found black soft material
of which I am not sure if it is graphite or not: I haven't taken any home, just used them to have fun and to draw pictures to the rocks.. The softness fits to pure graphite, but they are veryvery black. I have some pictures of some of them, just a minute..



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soft surface rubbed flat with a porcelain fuse
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Kara




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PostPosted: Nov 28, 2018 10:11    Post subject: Re: Massive graphite?  

here some pictures of the black thing mentioned above. Do these look like graphite?


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(too blue, it is greyblack)
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Pete Richards
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PostPosted: Nov 28, 2018 10:40    Post subject: Re: Massive graphite?  

It is quite clear that this is a rock, not the pure mineral graphite, but it certainly seems to contain a lot of graphite, as well as probably mica, quartz, and other things.

For this reason, hardness tests, specific gravity, etc. are likely to give ambiguous results, because they reflect the bulk composition of the rock, as well as properties of the mineral of interest, graphite, and the other minerals in the rock.

I think you've taken this about as far as you can. Good work!

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