If your home was built or renovated before the 1990s, it is difficult to guess the method of insulation chosen as there were numerous options: fiberglass batt insulation, blown in cellulose, sprayed polyurethane foam or even vermiculite.
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. The CHIP program provided grants to homeowners to increase insulation levels, thereby reducing energy consumption. Instead of buying batts of insulation, homeowners could buy bags of loose vermiculite and pour them into wall cavities and between joists in the attic.
Similar to mica, if you discover these granules between the joists of your roof, it’s a safe bet to say that it is insulated with vermiculite. If your home was built before the 1990s, your vermiculite may contain amphibole asbestos fibers.
Vermiculite from the Libby mine in Montana, USA (which at its peak accounted for 70% of the worlds vermiculite production) 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.