a species of clay much used in scouring woollen cloth and other stuffs. It occurs greenish, yellowish-gray, and bluish-gray, and sometimes it has a spotted appearance. It is dull, but assumes a fatty lustre when pressed with the fingers, is very soft, feels unctuous to the touch, and it melts into a brown spongy scoria before the blowpipe. In England it occurs in beds; the best is found in Buckinghamshire and Surrey. When good it has a greenish-white or greenish-gray colour, falls into powder when put into water, communicates a milky hue to water, and deposits very little sand when mixed with boiling water. It is used by fullers in taking grease out of cloth before the soap is applied. Its constituents are 53-9 silica, 10-0 alumina, 9-75 red oxide of iron, 1-25 magnesia, 0-5 lime, 24 water, with a slight trace of potash.