Bauxite is the key mineral used to make aluminum. Starting in 1894, Alcoa bought or leased the rights to all major bauxite deposits in the United States. By 1920, Alcoa owned the rights to enough bauxite to supply 500 years of aluminum production. (Alcoa was broken up in an antitrust case decided in 1945.) This is an example of a monopoly created by: control of a key input. product differentiation. network economies of scale. scarcity of resources