My brother lives in eastern ND but works in the western part of the state. A couple years ago he sent me some slick, heavy, chocolate brown rock that I made some nice points from - turned out to be Rainy Buttes petrified wood/chert which has a high iron content. I don't know exactly where he found it, but if he gets back that way he is going to pick some more of it up for me. If you do get in touch with a local geologist or a local rock club they may be able to direct you to an area where you could find some. Good luck, Rick B.