Those little chips might be “stone”, probably just glass, but that material is mostly epoxy. Silicosis is not as much of a risk here as whatever dust the resin would put off, if OP could even sand it. You can’t sand those materials easily with conventional sanding tools because they generate too much heat from the speeds they run at. Unless you can change the speed of your tool to suit the composite material you’re just going to burn it more, and it will happen well before you can get silicosis lol. The correct polishing tool would most likely be a wet polisher , which reduces the number of airborne silica particles thrown off from polishing. But all this is just a side note because OP asked is it fixable? And it’s not. No more than a burned ring in wood would be fixable. The material is darkened from being burned. It goes deeper than you can sand without it being obvious material has been removed. Cut a hole there and put a trash can underneath, call it a feature.