Cryolite (fluoride of aluminum and sodium), a mineral mined only in Greenland, was formerly used as an ore but is now utilized in the manufacture of alum and soda.
Alum (a sulphate) is made from cryolite or clays.
Corundum (aluminum oxide) is, next to the diamond, the hardest natural mineral. Canada, North Carolina, Alabama and India have mines of corundum. Emery is produced chiefly in Greece and Asia Minor. Corundum and emery are powdered for use as abrasives in wheels, sharpening stones, polishing powder and cloth.
Emery is an impure form of corundum.
Feldspar is a silicate of aluminum with other metals. It is mined in Canada, Pennsylvania, Connecticut, New York, Maine and Norway, and ground up for use in pottery making.
Clay is chiefly silicate of aluminum and other metals. Kaolin is its purest form. The properties of clay vary with its composition, as china clay, fire clay, pipe clay, brick clay. Clays are found in all parts of the world as a result of the decomposition of other rocks.
The location of manufacturing centers of pottery of all kinds and of bricks, is dependent on clay deposits. In pottery making, Ohio, New Jersey and Pennsylvania lead the United States. Abroad, fine china is made in France, Germany, Austria, England, Japan, and China.