Vermiculite is a naturally occurring mineral that is a light-weight, fire-resistant, absorbent, and odorless material. It has used to make numerous products, including attic insulation. Vermiculite attic insulation is a pebble-like, poured-in product that has been used in many older homes.
If you have loose fill vermiculite insulation in your attic, DO NOT DISTURB IT. Any disturbance has the potential to release asbestos fibers into the air.