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I'm note sure if it's an anthracite, augite, jet (lignite) or something completely different. I don't know where exactly i found it because it's from my old rock collection. I would appreciate your help with identification.

  • Colour: black
  • Texture: glassy
  • Weight: 25g
  • Hardness: 3
  • Location: Unknown (collection piece). Czech Republic.
  • Density: 2,5g/cm3

ruler in centimeters

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closed as off-topic by Semidiurnal Simon, Fred, Peter Jansson, BillDOe, Gimelist Aug 8 at 2:27

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions about rock identification requests are off-topic. For more information, see the announcement on meta." – Semidiurnal Simon, Fred, Peter Jansson, BillDOe, Gimelist
If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Welcome to the site. We are not accepting id-request questions from a picture. You may find other sites on the net where they do. If you wish to have an answer here, follow this guide and edit your question with the missing information. Here is an example of a question we would accept $\endgroup$ – Universal_learner Jul 12 at 10:14
  • $\begingroup$ Some info regarding weght,hardness and density, and also location, would be helpful. Was there more of it scattered around? $\endgroup$ – Michael Walsby Jul 12 at 10:42
  • $\begingroup$ Arnie, can you do the displacement test If so, we will have density and myself I will vote to reopen it. $\endgroup$ – Universal_learner Jul 12 at 11:45
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    $\begingroup$ i did the displacement test, the density is 2,5g/cm3 $\endgroup$ – Arnie Jul 12 at 12:10
  • $\begingroup$ Density is too low to piroxenes as augite and to high for coal rocks even consolidated. I would say it is obsidian or other volcanic glass, but the hardness is too low. Did you scratched it with a coin? Obsidian would be scratched by a knife but not by a coin. $\endgroup$ – Universal_learner Jul 12 at 17:00
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You almost got the answer yourself. The rock is definitely lignite. As a confirmatory test, you could scorch it with a blow lamp or put it on a fire. If it's lignite it will burn.

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