I found these two intriguing rocks on the UK's seaside. They have an unusual potato shape and copper/green color. Whrn knocked against each other, the sound is clear, metallic and the vibrations keep going for a second.

The bigger one is about 20cm in lenght, and they feel heavier than an usual rock.

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  • $\begingroup$ Please read meta.earthscience.stackexchange.com/questions/124/… and update the question accordingly. One thing you could/should have done already is mentioning the actual weight and volume (and thus, density). $\endgroup$ – Jan Doggen Aug 22 '16 at 10:40
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    $\begingroup$ I did read it and provided most of the info required there (minus density and hardness, which I could not determine) $\endgroup$ – Sam Aug 22 '16 at 11:09
  • $\begingroup$ Stop being right. You did not supply the weight and you did not supply the volume. Get a scale and a measuring beaker from the kitchen. Do you want an answer or not? $\endgroup$ – Jan Doggen Aug 22 '16 at 12:40

Break one open. If it is hard (scratches steel), black and vitreous, maybe with a conchoidal fracture, then it is flint, which is very common, especially in southeast England.

  • $\begingroup$ Ha, I don't want to break it. But indeed looks like flint, and it is from south-east UK. There's a place where it's chipped away and looks black and polished. $\endgroup$ – Sam Aug 22 '16 at 11:13

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