Every evening, Gayla's father came home from the mine covered in a fine white powder. So did the other miners in Libby.
Their wives shook it out of the work clothes and scrubbed it out in the wash. Their children breathed it while they played on the carpet.
The dust came from vermiculite, a mineral found in the mountains near town in 1919. Heated, it puffs up into light, shiny flakes, perfect for attic insulation and garden soil. It was sold as Zonolite.
Gayla's father, Perley, went to work at the mine in 1954. In 1963, the chemical company W.R. Grace bought it. By then it produced about 80 percent of the world's vermiculite, and at its peak it employed about 400 people.
Nobody worried much. The men were told it was just "nuisance dust." It was like farm dust, Gayla remembered them hearing: "You could eat a ton of it, it wouldn't hurt you."