What's in this stone I found at the beach?

This is a question from someone with zero significant geology knowledge.

but I do understand it can sometimes be impossible to identify minerals from a picture.

Found this at the beach and I dont know what these black veins are, couldn't find any pictures of anything similar with simple descriptions through google.

The black veins protrude slightly from the stone suggesting its something that erodes slower than the surrounding rock to me, the veins seem to go through the stone and doesn't seem to just be external markings.

Attachment image

3 Answers

  • 3 weeks ago

    It isn't obvious to me that it is sandstone. It looks more igneous in origin (a diorite or granodiorite: plagioclase feldspar-rich equivalent of "granite"). the black would be veins that filled fractures created in the rock long after it had cooled and solidified. Most likely from some sort of explosive fracturing (like perhaps when deep groundwater boiled as it rose and pressure dropped). The how of the fracturing is speculation. It is clearly a shattered rock, though, and the cracks that formed when it got shattered then got filled in by something else, which makes those dark veins. The picture does not allow me to see the veins well enough to ID the stuff filling the veins.

    My guess would be quartz, but I can't see it to be certain. quartz would be more resistant to weathering and erosion relative to plagioclase-bearing rock and thus the veins would stand up a bit compared to the bulk rock.

    Try reddit r/whatisthisrock. Should allow you to post a higher quality image than YA allows. A higher quality image is needed to look at the individual grains of the rock and to see what is filling the fractures.

  • Ron
    Lv 7
    3 weeks ago

    That is fractured sandstone. The cracks have been filled with a mineral cement. Since the veins are more resistant to weathering, I think it is probably a silica cement, likely chalcedony or chert. I have seen many examples of dark gray chert.

  • 3 weeks ago

    Those are symbols from Atlantis.

    • stephen3 weeks agoReport

      the other side is beautiful too, not sure on how I'd post a second picture up. It doesn't have the rings on the end like that side does but the veins are darker and more pronounced.

Still have questions? Get your answers by asking now.