Not to disagree for the sake, but, particularly on stones below 8 in hardness, the oxides are often thought to give a better polish. Some even use them on harder stones after 50K to "kiss" the polish and really bring it up. Some describe the diamond polish on these stones as being greasy or a bit cloudy. I'm surprised to hear of scratches with the wax sticks, as they are designed to eliminate the scratching that you get with slurries that get too dry. It's possible with iolite to be on or near a cleavage plane which can cause problems with polishing, and polishing at a stop is often the cure for that. The other possibility with scratches is that there was some subsurface damage that wasn't eliminated in the prepolish. In that case it isn't the cerium stick that is scratching, but the fact that it is polishing and revealing the scratches that weren't eliminated in the prepolish. Prepolishing a little longer would eliminate that. Just my two cents, but if you google for discussions on this, I think you will find what I say about oxides being best for anything but corundum and chrysoberyl being repeated elsewhere. Hope this helps.