Sepiolite is a clay mineral, a complex magnesium silicate, a typical formula for which is Mg4Si6O15(OH)2 • 6H2O. It can be present in fibrous, fine-particulate, and solid forms. It is used in oil drilling and also in a solid form known as Meerschaum for carving.

The name comes from a perceived resemblance of the material to the porous bones of the cuttlefish or sepia. On account of its low specific gravity, one to two, and its porosity, it may float upon water, hence its German name Meerschaum ("sea foam").

Owing to its fibrous mineral nature, sepiolite veins may contain the hazardous material, asbestos; even where asbestos is not present, sepiolite is often mistaken for it. Careful analytical techniques may be required to distinguish the two.