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These were found at to the top of a hill by McLaren park near the Blue Water Tower in San Francisco, in the dirt in the middle of the path.

They feel slightly heavier than normal (same size) rocks. The material is hard. After I cleaned them, you can see the surface reflection just look like metal (light gray color).

What kind of rocks are they?

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  • $\begingroup$ you need to give more information please take a look here earthscience.meta.stackexchange.com/questions/124/… and edit all the information you can into your question.atleast one of the "rocks"are man made and probably both are. $\endgroup$ – trond hansen Mar 31 at 5:23
  • $\begingroup$ I see, thanks for the reply, any idea what people made these "man made rocks" for? $\endgroup$ – Sammy82 Mar 31 at 6:47
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This is smelter slag. The green patina on it suggests it to contain some amount of copper.

I have absolutely no idea what it was doing at the place you found it.

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  • $\begingroup$ Are they both smelter slag? what about the other oval shape one? $\endgroup$ – Sammy82 Mar 31 at 7:49
  • $\begingroup$ I'm not sure if slag made in an actual smelter, but definitely artificial. People do all kinds of weird things: youtu.be/zVVJcoU7cHo $\endgroup$ – Gimelist Mar 31 at 7:54

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