Asbestos is a group of minerals found in certain types of rock formations. They are made of mineral fibrils that can be so small that is would take several million of them grouped together to make a fiber as big as a strand of hair.

Fibrils are so small they can only be seen with an electron microscope. If fibrils bunch together they are called fibers. Small fibers can only be seen by using a specialized optical microscope. When fibers bunch together they are called bundles. Bundles and large fibers can be seen without a microscope.