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Vermiculite and Asbestos

You may have come across something called “vermiculite” in potting soil or in attic insulation.  Why is it often associated with asbestos?

Vermiculite is a mineral that appears in a pebble-like form. It is often gray, silver, and gold in color and can shimmer in light. Because of its insulating properties and versatility, vermiculite was used in a wide variety of purposes such as insulation and potting materials. While vermiculite alone isn’t harmful, it can often contain asbestos.

The bulk of vermiculite found in US homes is directly from Libby, Montana. The EPA estimates that 70% of vermiculite sold between 1919 to 1990 originated from there. In the vermiculite mines, there was an asbestos deposit that formed alongside it. As the mineral was mined, large quantities of asbestos fibers were thrown into the air which caused many properties of Libby to become contaminated. While some of the asbestos content in Libby is regulated fibrous Tremolite, many of the asbestiform minerals found are known as Libby amphiboles, which are not regulated.

The term Libby amphiboles refers to two asbestiform minerals known as Richterite and Winchite. These minerals typical form from contact metamorphism of limestone. In their fibrous forms, they share similar physical properties to the regulated five amphibole asbestos minerals. There are no current federal regulations on Libby amphiboles although they may have similar health effects to other regulated types.

The EPA has spent hundreds of millions of dollars on the cleanup of Libby.  They recommend that if you find suspected vermiculite insulation in your home, you should assume it to be asbestos-containing. There are tests that can be performed, but they are more expensive than standard asbestos testing.  

 

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