cause of mineral or process similarities. Contrast to a mineral ‘by-product’ which is the residual of, or secondary to, extraction and production of a primary mineral of interest.

Critical minerals—Those that are both essential in use and subject to considerable supply risk.

Dielectric—A material in which displacement currents predominate over conduction currents (i.e., an insulator; Bates and Jackson, 1987).

Divalent ion—An atom that has acquired an electrical charge by gaining or losing two electrons.

Electric arc furnace—Steelmaking furnace in which scrap is generally 100 percent of the charge. Heat is supplied from electricity that arcs from the graphite electrodes to the metal bath. Furnaces may be either alternating current (AC) or direct current (DC). DC units consume less energy and fewer electrodes, but they are more expensive (

Froth flotation—A method of mineral concentration used in platinum group metal production that separates the various minerals in the feed according to their differing surface properties. Separation is achieved by passing air bubbles through the mineral pulp. By adjusting the chemistry of the pulp with various reagents, valuable minerals can be made aerophilic (air avid) and gangue minerals aerophobic (water avid). Separation occurs when valuable minerals adhere to the air bubbles that form the froth floating on the surface of the pulp (available online at; accessed September 27, 2007).

Galvanized steel—Steel coated with a thin layer of zinc to provide corrosion resistance in underbody auto parts, garbage cans, storage tanks, or fencing wire. Sheet steel normally must be cold-rolled prior to the galvanizing stage (About Metals Glossary).

Grade—The relative quantity or percentage of the commodity or element of interest in a unit volume of mineralized rock.

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