I had a colleague give me some blue green clay, from her property. It had quite a bit of debris in it. I slaked it down, and ran it through a screen, like Marcia suggested.
It was easy enough to work with, and I even through some things with it. When fired, it turned golden yellow. It survived to Cone 04 well enough. But it was weak at that temperature. The test tile I made, was about a quarter inch thick. I could snap it in half, once bisqued.
I never took it beyond 04. But in college, one of my classmates brought in a similar clay. The instructor fired it to at least Cone 6. It melted at that temperature.
I actually still have some of it left. I may use it again for something.