enter image description hereenter image description here I found this rock at a lake edge in Co. Sligo Ireland,its shiny black,leaves a black streak, weighs 320 grams displaces 125ml of water which gives it a density of 2.56 https://www.youtube.com/watch?v=ovdE_-FCWpc .Where I found this there is dark green serpentine,that looks like Antigorite.It has a hardness of around 3-3.5 about the same hardness of Calcite.It attracts a magnet on a string.A photo of the inside as its broken open(Top Photo)

  • $\begingroup$ it is very hard to see what it might be,is it possible to knock a chip of it and post a picture of the piece you removed. $\endgroup$ – trond hansen Dec 26 '18 at 10:18
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    $\begingroup$ Thank you for your comment trond hansen, I split the rock to see the interior, I have lots more of these rocks $\endgroup$ – Dave Dec 26 '18 at 15:31
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    $\begingroup$ Is it translucent with a back light? (Surprisingly some black stones are.) $\endgroup$ – Chloe Dec 27 '18 at 1:20
  • $\begingroup$ No its not translucent with back light, but opaque $\endgroup$ – Dave Dec 27 '18 at 10:52
  • $\begingroup$ Chipping serpentinites is not a good idea, some forms are also known as asbestos, and you don’t want to breath that in. $\endgroup$ – Gimelist Dec 28 '18 at 4:46