I simply don't know I found it in upper Neogene terignious sediments where this rocks are well presented. I am traying to understand, what kind is this rock in order to understand the direction of transport. Do you think that this could be bazalt.
It seems to have a conchoidal fracture so I guess that it an aphanitic volcanic rock..It could even be a flint clay of volcanic origin.
A meaningful determination of the rock only because of the photos shown is impossible. Photomicrographs from a petrographic thin section would be very useful for the determination.
Yes, better identification is only possible through petrographic study.....
I don't have the equipment needed for petrographic study. If somebody wish to help me I can mail the rock sample anywhere in Europe.
Miroslav, the others are correct in commenting on the paucity of information - and of course any rock with significant quartz or feldspar or a vast number of rock-forming silicates in it is harder than steel or glass. So first princioles. If you are working with rocks you need to identify minerals in them (impossible by eye if very fine-grained but this looks like it could be coarsely crystalline, although somebody else sees it is having conchoidal fracture). So get a x10 and x20 hand lens and tell us its grainsize. It is difficult with only access to field tools, but firstly hardness TGCFAOQTCD - 12345678910- so is it harder or softer than apatite, orthoclase, quartz or topaz? If it were basalt in a terrigenous sediment it would usually be weathered a bit and have secondary minerals that are usually coloured and have cleavage etc., and will leave a coloured streak on a face of broken porcelain. Finally you can measure its specific gravity easily, and this is much higher in say basalt than a quartz rock.
Just guessing - it could be a very fine-grained dark rhyolite or dacite lava. Generally these are paler, but I have seen very dark ones. It does not look like galena, and if it was galena it would be very heavy. As others have said, you need to do other tests. Measuring the specific gravity would be one test. Also try the hardness of the paler minerals that I can see.
Brian - you can add to that that detrital galena does not survive well :-) I have seen it claimed but the examples I have looked at have been replaced gypsum nodules in sandstone, Try what I said - eg galena is very high SG, has strong cubic cleavage, a black streak on porcelain, is relatively soft, fuses in a flame. Now try more likely candidates (it is unlikely as a rock to have such extreme attributes as a mineral like galena). And get used to doing most things under your hand lens - it gives grain size and individual grain colour, lets you scratch individual grains for hardness and streak colour, reveals crystal shapes, cleavage, alteration rims to other minerals easier to identify that give you clues to the original mineral....use x10 and x20 to get individual grains versus rock fabrics.
From the hand specimen photograph shared, the specimen appears to be melanocratic, aphanitic with traces of glassy material. From the appearance it appears to be Basalt rather than the andesite/ dacite or rhyolite. As indicated by Miroslav, its been found from Upper Neogene sediments which are part of Neogene-Pleistocene Basins of Macedonia wherein there are evidences of range of volcanic rocks from Andesite/dacite/rhyolite to basalts are documented. For more details please refer :
Dumurdzanov, N., Serafi movski, T., and Burchfi el, B.C., 2004, Evolution of the Neogene-Pleistocene Basins of Macedonia: Boulder, Colorado, Geological Society
of America Digital Map and Chart Series 1 (accompanying notes), 20 p (http://www.geosociety.org/maps/2004-dumurdzanov-macedonia/dmc001.pdf)
Ok I examine it and those are the results: very very fine grained, I saw at least one Quartz grain also there is some micro caves with feldspar inside I think, it has the same hardnes as Quartz, it doesn't leave any streak on ceramic plate. I am posting a picture from different sample of the same rock. It has prismatic shape.
Hey buddy, I would be glad if I can help out.
Your sample looks interesting and reminds me of coal and black shale.
If possible, try to make a thin section and upload some pictures here (Plane Polarized Light and Crossed Nicols).
Good luck.
Another possibility is silicified siltstone, maybe from an area of folded rocks.
Speciphic Gravity 2.4-2.6. On second look it can be metamorphosed shale, siltstone. The minerals inside the micro caves are Quartz or Calcite
OK - so that immediately removes possibilities like coal (1.2) and basalt (2.8 to 3.0) that some have suggested. So it could be any fairly siliceous rock - black chert, rhyolite, andesite. siltstone, hornfels afer a siliceous rock like siltstone. If it were hornfels after shale it would probably be full of micas and easily scratched, although you still have not mentioned its accurate hardness. So do you have a piece of quartz (hardness 7 on Mohs scale), a piece of apatite (5), and a pure cleavage fragment of orthoclase (6). So scratch it with each, or scratch them with it. If it is between orthoclase and quartz in hardness it will not help you much. But if it is between apatite and orthoclase it would suggest other minerals such as micas, so things like hornfelsed shale would be a possibility. I have gone through this in detail, because these and colour (which often does not reproduce well in screen images) are the sort of things you need to tell people when you first post a photo for identification. Most people do not, so they have no hope of getting a very sensible or useful answer. I would guess a black chert or a dark felsic lava or a siliceous hornfels as possibilities - have you checked it under your x20 hand lens for small phenocrysts? I hope that helps you and others for the future. You say you lack petrographic facilities - do you also lack XRay and analytical facilities? SiO2 % would help, as would K20, Na20, Cao. MgO
Martin is quite right. As there are only limited data the guess work can be unlimited. The least important information is the "color:, i.e. black. There are flint clays of acidic volcanic origin that are black due to organic matter. An x-ray analysis to see if there is a lot of fine-grained kaolinite in the rock might be helpful. This would explain the conchoidal or sub-conchoiddal nature of the rock. Best wishes, Paul.
So far we know the following facts: It is harder than steel-6.5 But can not scratch Quartz and Quartz can not scratch it. So the hardness is 7. It has black color. It has SG of 2.4-2.6. It doesn't leave a streak. It doesn't react with acid. It is very fine grained. On second sample very fine cleavage can be observed. It has small veins with Quartz probably formed secondary during metamorphoses.
As a result I think that this is a slate and the hardness is due to flint that is formed During the metamorphoses.
Well, strictly hornfels perhaps not flint - flint has a more specific meaning Miroslav. But you know more than when you began :-) Paul, I agree that colour is the least important, but if it were say dark green (and lots of men have trouble with distinguishing green and brown, and poor image reproduction can make it look very dark grey because it is their mist common colour blindness) one might expect some other possibilities involving green minerals. And the enquirer can see the colour so it is no extra work. My message being that such enquiries need the enquirer to do all their home work before posting an enquiry, and I am not sure that these basic approaches are always still taught, because we pampered geos with access to equipment in First World laboratories simply x-ray, probe and thin sections. I work in some obscure places and also often want to have some idea what I am looking at while still there. Hence my attempt at mentoring :-). Amazing what you can do with a flame platinum wire, borax and a blow-torch as well, but you would have to be permanently in such a place to bother, and I think those skills are pretty much dead and superfluous (but they are easy with things like K-rich rocks etc - emission spectroscopy by bunsen burner). And yes, I missed mentioning fracture, although flint, rhyolite and horfels can all give that.
Yes, I'm a bit of a dinosaur - it was great when AAS took over from paper chromatography :-)
Thank you dear all for your answers. Now I certainly new more, than before I asked this qeustion. I will use more systematic approach in the future. Thank you again.
You are welcome Miroslav. And yes Paul, X-ray work would be useful as it would also tell if one was looking at a quartz, felspar or phyllosilicate-rich rock,
Kenneth, we are definitely much better off now though - until we have to cope without expensive and advanced equipment. However I have been surprised when I have seen people fail to use a powder camera at all when only minor material was available. I also miss having a good hardness-reflectance set-up for sulphide mineragraphy - so rapid and such good optics prior to sampling a point. So often I see people assign a mineral species on the basis of a probe analysis alone, with no x-ray crystallographic verification (on one occassion I had to point out that there were actually 4 minerals with that composition). Petrography is also not what it was, but it is quite a time-consuming skill to learn and optics is physics (yuk prof. - we did geology to avoid that and maths!). However geology has so much breadth compared to our day, so it was easier for us to go into much more detail in learning some skills, and the basic sciences and maths were pre-requisites to a reasonable level. Join the grumpy old geo-men club!
I knew an elderly geologist once (in his 90s in the 1970s), who used to tell me about his field trops for months using camels, ice-climbing glaciers in Greenland with ladies in ankle-length skirts, and his dubious exploits in Montmartre - time moves on.....
I am not sure if that is a phenocryst in the rock. It could just as well be an altered phenocryst of a completely different composition..It would help to know if it is feldspar or something else.
Hi, Miroslav,
My suggestion is to send the specimen to the Sofia University, Department of Mineralogy, Petrography and Economic Geology in Sofia. Thin section could be done there and my colleagues would help you in the diagnosis. It is not so difficult and far from your University.
Borislav - that seems an obvious solution - I was only suggesting alternatives like XRay because most places with a chemistry department would have them. Also, there are many places that manufacture thin sections from rocks quite cheaply, and I inagine Miroslav has a petrographic microscope?
A piece of the rock can be ground up and one should be able to get an oxide analysis of the rock that should tell you a lot about the origin of it. (e.g. acidic or basaltic or neither). There are many labs that do this. I might be able to help as I have a few contacts left in the U.S. Geological Survey. Let me know.
Ken, No it wont but it will tell you if t is acidic or basic in composition, if it a volcanic rock as I suspect.. Also it is possbile to analyze the glass inclusions in the minerals by electron microprobe if it is volcanic.in origin.
Kenneth, the original question was what type of rock, and of course many labs will do a full rock analysis, we do that all the time - the discussion of minerals was simply as a means to decipher the type of rock. Often part analysis by ICP will be sufficient for the purpose (cheaper, fewer elements) but one must choose an appropriate sample digestion for full sample digestion. The problem (like thin sections, petrography) is that the places I would reccomend would cost a fortune to send a single sample from Bulgaria for one-off analysis and preparation. However I imagine all these things might be available in Bulgaria.
Miroslav is a PhD student - it is obviously difficult if the unversity has no petrography, chemical analysis or XRay facilities and I am a little surprised, but he is in the Department of Geography, Ecology and Environment Protection and his publications are geotechnical eg landslides (I think Miroslav?). So this is a one-off question by someone not equipped for other types of studies. However he needs to find somewhere nearby in his own country to get assistance (I think someone has already offered here - if not, Miroslav, get on the telephone to other geology departments in your country - and good luck).
Martin - the distance between the town of the Miroslav's university and Sofia University, also in Bulgaria, is only two hours driving. Everyone of my colleagues there could help free to Miroslav, I am sure. He could even sent a small chip of the rock to the Department of Mineralogy, Petrology and Economic Geology and describe in e-mail what he want. It is more than easy.
Up to you Miroslav - you have willing associates in your own country! I was confident that the Bulgarian geological fraternity was much the same as here Borislav :-)
Thank you professor Kamenov. I will be more than great full if you can help me with determination of few rocks samples. If you let me I would like to send you e-mail in order to discuss what is the most convinient way to handle you the samples. Thank you in advance
My e-mail at home is: [email protected]. You can mail me any time.
This is more of volcanic origin.. I am afraid you will have to engage in petrographic studies. As for the purpose of your study you could really use Cross lamination, Pebble imbrication and ripple mucks if any to construct the direction of sediment transportation and you could end up creating Rose diagrams from the ripple data
From the photographs, to me they appear like somewhat transported basalt pieces. If you can send a sample or thin section of the same to me I probably will be able to identify and name it. You may write to me at [email protected]. Since you are in a position to send the sample to anyplace in Europe, you can as well send it to India. Identification of a transported rock piece in hand specimen is not that easy and more so from a photograph. Though petrography is not an end in itself, it is a means to an end. However, I feel the identification of the water worn and transported pieces may be due to your scientific curiosity and may not be directly related to your research. .Best of Luck. K.N.RAO
Based on megascopic features...its, fine grained, hard compact massive, melano cratic igneous rock probably volcanic origin.
It need not be a basic rock like basalt as suggested as basalts easily weather and wont be this hard as you have mentioned.
It probably be a silica bearing or silica saturated rock like obsedian?.
A simple thin section or chemical analysis will give you first hand confirmation.
It is almost certainly rhyolite.....perhaps a tuff that has devitrified. Lots of rocks that look like this in the Precambrian
Dear David,
I've sent few samples from this and some other rocks to Professor Kamenov from Sofia University. He will analyse the samples and as soon as posible I will post the results back here.
Best regarsd: Miroslav
Dear colleagues,
Thank's to professor Kamenov efforts I have the petrographic analysis of the sample and the result is very interesting. It turns out that the sample is:
Pseudotachylite or Pseudotachylyte( original speling), proto base is a slate.
Not easy to guess without the geological setting. Fault zone or impact structure?
Most likely it is a result of some fault zone, but you are definitely right that without knowing the geological setting it is not recommendable to make any conclusions judging only from a photo or even a single specimen.
This specimen is found in the North part of Blagoevgrad Graben, SW Bulgaria. In Neogen terrigenious sediments, deposited probably by paleo braided river ( according the Geology map of the area -Lower Neogene, but after some new avidence most likely upper Neogen). Such rocks are not presented or haven't been found in the South part of the graben or neither in the younger sediments.
There is numerous modern faults that are crosing the area including Struma fault zone, but so far I haven't seen such rocks along it .
I am not aware of impact structure in the proximity of the area of deposition.
There is one siutable spot, but I have to go and check it.
Regards
Miroslav
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