Fuller's Earth

Fuller's Earth, a mineral consisting chiefly of silica, alumina, and water, with a little magnesia, lime, and peroxide of iron. The silica is about 53, the alumina 10, and the water 24 per cent. of the whole. It is regarded as essentially a hydrous bisilicate of alumina. It occurs in beds, associated with chalk, oolite, &c.; is usually of a greenish-brown or a slate-blue colour, sometimes white; has an uneven earthy fracture and a dull appearance; its specific gravity is from 1.8 to 2.2; it is soft enough to yield readily to the nail; is very greasy to the touch; scarcely adheres to the tongue; falls to pieces in water with a hissing or puffing sound, but does not become plastic. It has a remarkable power of absorbing oil or grease; and was formerly very much used for fulling cloth (see WOOLLEN MANUFACTURE), for which purpose it was considered so valuable that the exportation of it from England was prohibited under severe penalties; it is still used to a considerable extent. The annual consumption in England is said to have at one time exceeded 6000 tons. It is found at Nntfield, near Reigate, in Surrey, in cretaceous strata, where it forms a bed varying in thickness from less than 8 feet up to 12 feet or more. The lower part of this bed is blue, but, owing to the peroxidation of iron, the upper portion is buff-coloured—the change being brought about by the infiltration of water. It is also found in Bedfordshire, Nottinghamshire, Kent, Surrey, and elsewhere. There is a considerable deposit of it at Bath, where the group of associated blue and yellow clays and marl has received the name of 'the Fuller's Earth Series,' belonging to the Jurassic system. It is also found at Maxton in Scotland, and at various places on the Continent, as in Saxony, Bohemia, and near Aix-la-Chapelle.