Region 8

ABCs of Asbestos

microscopic asbestos fibers
Microscopic asbestos fibers
tremolite rock
Tremolite rock
popped vermiculite
"Popped" vermiculite

Asbestos is made up of long, thin fibers that are strong and heat-resistant. Asbestos has been used in thousands of products (such as building materials and heat-resistant fabrics). The fibers do not readily dissolve or breakdown and individual fibers are too small to be seen with a naked eye. The fibers can become airborne, and eventually settle onto soil, sediment and other materials both indoors and outdoors.

Please visit EPA's Asbestos website for more information about asbestos.

Amphibole asbestos describes the mineral family that includes Libby Amphibole asbestos (LA). LA is a distinct form of asbestos and contains a mixture of six different Amphibole minerals. LA was co-mingled with vermiculite, a silver-gold to gray-brown mineral that is flat and shiny in its natural state and puffed and dull in its expanded shape.

What is Vermiculite?

Vermiculite was discovered near Libby in 1881. In 1919, Dr. Edward Alley found that vermiculite expanded (or "popped") when heated. This created pockets of air that made the material suitable for use as insulation or as a soil amendment.

Dr. Alley founded the Zonolite Company and developed the mine and processing facility north of Libby, producing expanded vermiculite as Zonolite. Zonolite was lightweight, sturdy, and inexpensive. It was used in everything from construction materials to school craft projects.

It is estimated that the Libby mine was the source of over 70 percent of all vermiculite sold in the U.S. from 1923 to 1990; and, over its lifetime, it employed more than 1,900 people. W. R. Grace bought the mine and processing facility in 1963 and operated it until 1990.

Is vermiculite contaminated with Libby Amphibole asbestos still being used today?

  • Vermiculite from the former Libby vermiculite mine is no longer commercially available.
  • A formerly used commercial insulation product called “Monokote” was produced with vermiculite ore from the Libby Zonolite mine and has been known to be a source of LA.
  • In Libby and Troy Montana, vermiculite and ore from the Libby mine was occasionally seen as decorative landscape rock or driveway material.
  • The asbestos fibers observed in the vermiculite ore are a waxy-silky white to greenish white, with fibrous strands running across the surface.

The vermiculite from the Libby mine was contaminated with a highly friable form of asbestos called Tremolite-Actinolite Series Asbestos, often called Libby Amphibole asbestos (LA).

The asbestos veins in the ore body have contaminated much of the material taken from the mine. Milling removed much of the asbestos from the finished product, but in many cases significant amount remained. Because asbestos fibers are so small, this contamination is not evident with the naked eye.

Not all vermiculite is contaminated. However, it is difficult to visually distinguish Libby vermiculite from other vermiculite; therefore, all vermiculite should be handled with care.