Fuller's Earth

Soft, greenish-grey rock resembling clay, but without clay's plasticity.

It is formed largely of clay minerals, rich in montmorillonite, but a great deal of silica is also present.

Its absorbent properties make it suitable for removing oil and grease, and it was formerly used for cleaning fleeces (‘fulling’). It is still used in the textile industry, but its chief application is in the purification of oils.

Beds of fuller's earth are found in the southern USA, Germany, Japan, and the UK.

From http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0015246.html