Anyone know what kind of rocks these are? I found them at a yard sale. They're very smooth and dull in color, nothing sparkly or bright...

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JoyfulSilence · 51-55, M

I cannot tell. I am no expert.

But it looks like a few places have conchoidal fracture, common on quartz and glass:

Yet there are lines in it. I wonder if it is wood grain from petrified wood?

Tumbleweed · F

@JoyfulSilence they are identical to those! Thank you!! I found some rocks awhile back and finally found out that they're actually slag.