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ABCs of Asbestos
Asbestos is made up of long, thin fibers that are strong and heat-resistant. This has led to its use in thousands of products (such as building materials and heat-resistant fabrics). The fibers do not dissolve or breakdown in any way. They can remain airborne for quite some time, but eventually settle into soil, sediment, or other materials (e.g., carpet).
Please visit EPA's Asbestos website for more information.
Amphibole asbestos describes the mineral family that includes Libby asbestos. Amphibole asbestos fibers are generally straighter and break apart more easily than other asbestos fibers. They are also believed to be more toxic than fibers from other types of asbestos.
Libby amphibole asbestos (LA) is a distinct and relatively uncommon form of asbestos.
- It is not a commercially viable mineral, but a contaminant in the vermiculite ore from the Libby mine.
- Individual fibers are too small to be seen without a microscope.
- Asbestos ore is occasionally seen locally, usually as decorative landscape rock or driveway material.
- The ore is waxy-silky white to greenish white, with fibrous strands running across the surface.
Vermiculite and Zonolite
- Vermiculite is a silver-gold to gray-brown mineral that is flat and shiny in its natural state and puffed and dull in its expanded shape.
- It 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 Zonoliteä. Zonoliteä was lightweight, sturdy, and inexpensive. It was used in everything from construction 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.
The vermiculite from the Libby mine was contaminated with a toxic and 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 most, if not all, of the material taken from the mine. Milling removed much of the asbestos from the finished product, but a 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 distinguish Libby vermiculite with the naked eye, and all vermiculite should be handled with care.