Where does asbestos come from?

Asbestos is a naturally occurring mineral found in metamorphic rocks. It forms when mineral crystals grow in cracks (often called veins) found in soft rock formations. The width of the vein across which the asbestos fibers grow determines their length. Canada and South Africa are the largest sources of asbestos, but there are significant asbestos deposits in the United States, as well. The largest U.S. asbestos deposits are found in the western U.S., as well as North and South Carolina. Most asbestos found in the United States and Canada is white asbestos, or chrysotile. Brown asbestos, or amosite, is generally found in Africa, while blue asbestos, or crocidolite, is found in South Africa and Australia.
Although asbestos can be found in the United States, it has not been mined here since 2002. Any asbestos still used in manufacturing in the United States is imported. Canada is our largest source of imported asbestos, although we do import a small percentage from Zimbabwe and other countries.

The asbestos production process begins with locating deposits of asbestos-containing ore. A magnometer, a type of magnetic sensor, is often used to locate such deposits, because asbestos (particularly chrysotile) is often found near the magnetic mineral magnetite. Core drilling is then used to determine the size, level of purity, and exact location of the deposit. The asbestos-containing ore is then mined using conventional mining methods. Different types of asbestos are generally found at different depths, so mining practices may vary depending on the type of asbestos.

After the asbestos-containing ore is mined, the asbestos fibers must be separated from the ore. Because the asbestos fibers and the ore have a similar chemical composition, they cannot be separated using chemical methods. Instead, physical methods of separation must be used, the most common of which is called dry milling. Dry milling involves using a vacuum to suck the asbestos fibers out of the ore, then crushing the remaining ore into small particles so that it can be sifted to separate it from the asbestos fibers. The crushing and sifting process is repeated several times with increasingly small particles. Other separation methods may be used as well.