My guess, based on my vague memories of learning about geology, is that those might well be metamorphic rocks created from heavily compressed sedimentary rocks, but I might well be wrong.

My main trouble with sedimentary rocks is that they tend to have bits that vary wildly in hardness. I can't remember all the types of sedimentary rocks, but I'm sure that conglomerates and sandstone don't work. I suspect that some others would only work if treated very, very carefully and tumbled only with rocks that were like them in hardness.