What is Vermiculite?

Vermiculite is a silver-gold to gray-brown mineral that is flat and shiny in its natural state. When heated to around 1000 degrees C, it pops (or puffs up) which creates pockets of air. This expanded form, and the fact that vermiculite does not burn, made the material suitable as an additive, for example to potting soil. It also made a good insulating material.

Vermiculite insulation was a popular material in the 1940s and continued with the energy crisis into the mid-1980s. In Canada, it was one of the insulating materials allowed under the Canadian Home Insulation Program from 1976 to the mid-1980s.

So what’s the big deal?

Vermiculite from the mine in Libby, Montana is known to contain high levels of amphibolic asbestos. Extracted from the mine between 1920 and 1990, this vermiculite insulation was sold in large bags mainly, but not exclusively, under the trademark Zonolite® Attic Insulation. The mine was closed in 1990. As well as being rich in vermiculite, this mine had the misfortune of having a deposit of tremolite, a type of asbestos. When the vermiculite was extracted, some tremolite came in with the mix.

For Canadian use, the raw product from the Libby mine was shipped to processing plants in Montreal, St. Thomas, Ajax and Toronto, and Grant Industries in western Canada. At these plants, it was processed and sold as Zonolite. In its good years, the Libby mine accounted for more than 70% of the world’s vermiculite production.