Ceramics come in a wide variety of shapes, from blocks and heavy wedges to flake-like shards. They're all more costly and less common than other abrasive minerals. All of them are very tough and very aggressive.
Like silicon carbide, ceramics are not friable, and do not renew their cutting edges when sanding wood. But they don't dull as quickly because of their extreme toughness. This makes them the best choice for hogging off stock, roughing out shapes, removing finish and leveling uneven boards. For this reason, they are generally available only in coarse-grit cloth belts for stationary and portable sanders.
Ceramic mineral names and the trade names they're sold under are not easy to sort out. Though Cubitron sounds like a trade name, it's a ceramic mineral. One of its trade names is Cubicut. When mixed with aluminum oxide, it's sold as Regalite. Alumina zirconia is the name of a ceramic mineral. Sometimes it's marketed as aluminum zirconia, as if it were another type of mineral. It's also sold under the trade names Norzon and AZ as a ceramic mineral.
Abrasive manufacturers make these names intentionally confusing to avoid losing their copyrights. If a trade name becomes synonymous with the product in the public's mind (think of a thermos), then any company can use it.
Garnet is the only natural abrasive mineral still widely used for woodworking. Like aluminum oxide, it is blocky in shape. Unlike aluminum oxide, it is non-friable, not very tough and dulls very quickly. This is not necessarily a defect. The softer cut of a garnet paper, though slow, will produce the smoothest finish of all the abrasives within a given grit size. Because it is so soft, garnet will not leave pigtail-like scratches the way an aluminum oxide will when used on a random-orbit sander. This makes it well-suited for final sanding of wood surfaces.
Garnet is an excellent choice for final sanding end grain and blotch-prone wood. Garnet's peculiar tendency to burnish wood--close off pores--makes a stain penetrate far more evenly though less deeply.
-Strother Purdy is an assistant editor of Fine Woodworking. Photos by Strother Purdy. Drawing by Tim Langendorfer. From FWW #125, pp. 62- 67.