We do not know alot about this material, apparently it appears in recipes from South America. We have arbitrarily estimating an LOI based on the analysis.
In one glaze recipe we saw, these were no other clays, so this is probably a clay. It has very low flux content, so it is likely refractory. It has an LOI like a kaolin, but the chemistry is more like a ball clay. So to substitute for it you could try 50:50 kaolin:ball clay.