Anyone know anything about rocks?

[Sewbean]

We found these on a beach recently. Why would they have these funny patterns on them? They are really pretty. Do they naturally look like this? We do often find nice pieces of broken pottery on the beach so maybe they are manmade.

Can't help but I love the title of your post.

Possibly volcanic? Love a good beach stone

Love a good beach find! Geologist husband says it's impossible to say for certain without seeing them in person but likely to be rock that has soaked up oil over a long period, so effectively an oil stain.

I knew someone on here would know! Thanks