Paco Joyner, age 14, of Marion, Ohio, for his question:

WHAT IS AN ABRASIVE?

An abrasive is a substance used to grind, smooth, sharpen or polish
various materials. Abrasives include sandpaper, emery cloth and grinding wheels.

Ancient peoples used abrasives to sharpen stone tools and to polish metals, gems and marble. Natural abrasives include such items as emery, pumice and diamonds.

Abrasives form one of the most important materials used by modern industry, especially in the glass, flour, leather, lumber, steel and building industries. Most industrial grinding is done by manufactured abrasives such as silicon carbide and aluminum oxide.

Both natural and manufactured abrasives are crushed to degrees of fineness, ranging from fine powders to coarse grains. Often the grains are pressed together to form grinding wheels and sharpening stones. They may also be glued to a cloth or paper backing to form abrasive sheets or belts for polishing and grinding.

The sharpening abrasives, such as diamond dust, are used mainly to sharpen the carbide tools used to cut steel, aluminum alloys and other metals.