Vermiculite is a mineral that sometimes contains trace amounts of asbestos and silica. According to the UK-based Vermiculite Association, “asbestos fibers are a potential risk to health, and in the past there has been some vermiculites contaminated with trace amounts of asbestiform material.” That said, if vermiculite remains undisturbed in the attic, it’s considered safe. Risk does become an issue, however, during renovations or any activity that could disturb the vermiculite. Professional sampling and testing of house dust is one way to know whether or not the vermiculite is staying put.