The lighter color ones are what I think you have but a higher quality. I find what I would call nodguals of it that are from very grainy to pretty slick. Unfortunately the slick ones are almost always broken up and freeze cracked.
The darker ones are from chert balls. They are like opening a. Dry hard to open box of chocolates. You never know what's inside. Could be slick, could be mixed half concrete.
Bjrogg