From Libby vermiculite, two classes of asbestos: serpentine and amphibole

The following section provides an overview of toxicity and health effects associated with Libby asbestos.

Vermiculite is a non-fibrous, platy weathered mica mineral type used in many commercial and consumer applications. Raw vermiculite ore is used in gypsum wallboard, cinder blocks, and many other products, and exfoliated vermiculite is used as loose fill insulation, as a fertilizer carrier, and as an aggregate for concrete. Exfoliated vermiculite is formed by heating the ore to 10,000 -18,000 degrees F, which explosively vaporizes the water contained within the mineral structure and causes the vermiculite particles to expand from 6 to as much as 30 times their original volume.

Over time, vermiculite from Libby was found to be contaminated with several types of asbestos fibers. Asbestos is a general name applied to a group of silicate minerals consisting of thin, separable fibers.

Asbestos minerals fall into two classes – serpentine and amphibole.

Serpentine asbestos has relatively long and flexible crystalline fibers; this class includes chrysotile, the predominant type of asbestos used commercially.

Amphibole asbestos minerals are brittle and have a rod- or needle-like shape. Regulated amphibole minerals include crocidolite, amosite, and the fibrous forms of tremolite, actinolite, and anthophyllite. Other amphibole minerals, however, including winchite, richterite, and others, can exhibit fibrous asbestiform properties.