Vermiculite is a naturally occurring mineral (magnesium-aluminum-iron silicate).

Vermiculite is lightweight, non-toxic, and sterile and does not deteriorate over time. It has a neutral pH.

Vermiculite can absorb three or four times its weight in water and also attracts various plant nutrients such as potassium, magnesium, and calcium. These qualities make it useful for propagation and for potting up plants that do best in moist compost.