I found this rock at my friend's summer cottage in Finland. I have never seen a rock like this in my life. It resembles a lava stone, but Finland isn't a volcanic country. I am no expert in geology can someone help?

Update: So I once again visited my friends summer cottage and I remembered that I was advised to take a sample from the stone I found. I hammered too little pieces off the rock. It's completely dark from the outside but from the inside it's like a normal stone. I also rubbed it on to unglazed porcelain and it left a dark black streak like a piece of coal. So if you have any ideas what kind of stone this might be, give me your opinions?

Here are some pictures:

The big black one is the stone. The big black one is the stone.

This is how the surface looks. This is what the surface looks

This is how the stone looks inside. In the picture it looks more than it really is. This is what the stone looks inside, in the picture it looks more than it really is

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    $\begingroup$ It could be a mouldy dog poo. Are there any more pictures? $\endgroup$ – Siv Nov 29 '15 at 21:54
  • $\begingroup$ Can you break it open so you can see a fresh surface? If you take it and rub it on unglazed porcelain like the bottom of a piece of pottery, what colour is the streak left behind? $\endgroup$ – haresfur Nov 29 '15 at 22:03
  • $\begingroup$ Well I need to study more when I go there again...not a dog poo though (don't know if you were sarcastic):D. Thanks for answers. $\endgroup$ – Oneprime Nov 30 '15 at 11:07
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    $\begingroup$ Stack Exchange has had a number of questions like this. In every case we have a photograph that is too indistinct to say anything useful. I think the organizers need to issue some rules, such as a requirement for a scale bar, close-ups of both freshly fractured and weathered surfaces, additional information including hardness and density, and some clues regarding provenance. Otherwise it's like trying to guess the final picture from a single piece of the jigsaw. $\endgroup$ – Gordon Stanger Dec 1 '15 at 13:37
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    $\begingroup$ There is a guide $\endgroup$ – Jan Doggen Jan 1 '16 at 12:46

It is always hard to tell without seeing the actual rock but it appears from the fresh surface to be a mixture of dark grey/black and light grey/white crystals that are prismatic in shape - with rectangular cross sections. Thus it seems to me to be a mafic (meaning dark) intrusive (not erupted to the surface but cooled slowly underground so the crystals had time to grow) igneous (formed from a melt) rock. The dark crystals would be pyroxene and the light plagioclase making it the rock called gabbro. If you have a look at a geological map of Finland you could see if there is any gabbro in the area. I found this one:

geological map of Finland

  • $\begingroup$ I will look into that when I'm at home, and get the exact location of the place,thanks:) $\endgroup$ – Oneprime May 16 '16 at 8:23
  • $\begingroup$ I agree. Definitely looks like a gabbro, or something similar. $\endgroup$ – Gimelist May 16 '16 at 10:24
  • $\begingroup$ I took a look at the map, and there is gabbro in the area. So it's pretty surely gabbro, thanks for help. $\endgroup$ – Oneprime May 16 '16 at 16:55

It looks like slag from a furnace/metal working

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    $\begingroup$ Please expand the answer to explain your reasoning $\endgroup$ – arkaia Dec 2 '15 at 19:20

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