Sandpaper abrasive is a material used to smooth surfaces by abrasion. It is usually made from a combination of materials such as aluminum oxide, silicon carbide, or GARNET, which is the answer to this crossword puzzle. GARNET is a mineral that is mined from the earth and is known for its hardness and durability. It is often used in sandpaper abrasives because it can effectively remove material from a surface without damaging it.