Yeah, I vote for agate also.It was a trade Item all along the western end of the Missouri river. I found points,tools and debitage all along the south bank of Fort Peck Reservoir in east montana. That whole area is an archy site. Someone coulda jumped in a canoe and went visiting,or; Someone got to far west and got an arra in the a$*..for thier trouble and took it home. Ha ! Nice find ' Frank