My daughter found this large (about the size of her head) and very heavy dark gray/black rock with small craters in it and has iridescent coloring through the middle. If you could possibly help us identify it we would appreciate it.

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  • $\begingroup$ Hey, make sure to check out this link to when asking rock id questions: earthscience.meta.stackexchange.com/questions/124/… $\endgroup$ – tox123 May 5 '18 at 0:25
  • $\begingroup$ I agree with michael on that being slag. Its often found along the side of roads or train tracks. $\endgroup$ – Armondo Villaescuza May 6 '18 at 4:38
  • $\begingroup$ I've never seen a piece of slag that solid before, it almost looks like basalt that's a cool find even if it's not really a rock. $\endgroup$ – Ash May 8 '18 at 15:52

Your rock is slag, an artificial man made object. The holes used to be gas bubbles when rock was liquid. The iridescent colours you see are a result of slow cooling of the metal, allowing a thin layer of oxidation to form on the surface.

  • $\begingroup$ Thank you! I let my daughter know and she still thinks it’s cool. Lol $\endgroup$ – Bonnie Smoot May 5 '18 at 20:33
  • $\begingroup$ @BonnieSmoot of course it’s cool! It still used to be some sort of lava, even though man made. $\endgroup$ – Gimelist May 6 '18 at 1:47

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