There's washitas, and then there's washitas. Essentially they were the grade of stone which couldn't be sold as one of the better Arkansas grades, and they come in quite a variety. Generally they're quite low grit as pedro says and tend to have a few inclusions. For a while I used one as a bevel setter mostly because it's enormous and to hand, but somehow it seems to promote crumbling. It's worth playing with, but probably best as a knife hone if my experience is anything to go by.