John I have not competed in many years. Sorry for the confusion. I thought about trying again this year but it is not going to happen, too rusty. I am having trouble seeing those tiny facets on this years Grandmaster stone. You are correct that Matrix and cerium is only used on quartz or similar material. I have a lot of Bytownite I bought by the pound years ago and it polishes nicely with cerium on Matrix as well. Bytownite cuts and polishes and great looking stone. Diamond, 50,000, after 3,000 prepolish on a Batt, for everything else. I now use the good old red cerium. On a Matrix and with red cerium it only takes a small amount which lessens the one fault of oxides, the mess. After seeing Aussies polish opal with red cerium on youtube I quit using the more expensive French cerium. Red works faster as well.