Vermiculite is a natural mineral, expanded in a heating process.

Vermiculite has many uses, but is of interest in horticulture due to these attributes:
* Inorganic, and sterile.
* No known toxicity or fire hazard.
* High water holding capacity.
* Absorbs excess nutrients.
* Facilitates re-wetting.
* Low alkalinity.
* High cation-exchange capacity.
* Does not deteriorate in storage (if kept dry).
* Free from disease, weeds and insects.
* Good air holding capacity.
* Insulates and minimizes soil temperature fluctuations.

It is used in seed raising mix and propagating mix to allow good root development.