I got a few pieces of this from an estate and it took me a couple years to identify it. It kinda looked like a lot of jaspers, but nothing that I felt truly described it. Then I came across a small slab of the stuff with a piece of masking tape on it. In faint pencil, written on the aged and crumbling tape was the word, 'mozarkite.'
Full of a wide spectrum of pastel color, this material cabs up to a high polish. It's like a pastel version of butterfly jasper with a more diffuse patterning. It is a type of chert and is the official state rock of Missouri (who knew?)
For more information on Mozarkite, visit the Wiki page.