Industrial Minerals

Industrial minerals is a term used to describe naturally occurring non-metallic minerals that are used extensively in a variety of industrial operations. Some of the minerals commonly included in this category include asbestos, barite, boron compounds, clays, corundum, feldspar, fluorspar, phosphates, potassium salts, sodium chloride, and sulfur. Some of the mineral mixtures often considered as industrial minerals include construction materials such as sand, gravel, limestone, dolomite, and crushed rock; abrasives and refractories; gemstones; and lightweight aggregates.

Asbestos is a generic term used for a large group of minerals with complex chemical composition that includes magnesium, silicon, oxygen, hydrogen, and other elements. The minerals collectively known as asbestos are often sub-divided into two smaller groups, the serpentines and amphiboles. All forms of asbestos are best known for an important common property—their resistance to heat and flame. That property is responsible, in fact, for the name asbestos (Greek), meaning unquenchable. Asbestos has been used for thousands of years in the production of heat resistant materials such as lamp wicks.

Today, asbestos is used as a reinforcing material in cement, in vinyl floor tiles, in fire-fighting garments and fireproofing materials, in the manufacture of brake linings and clutch facings, for electrical and heat insulation, and in pressure pipes and ducts.

Prolonged exposure to asbestos fibers can block the respiratory system and lead to the development of asbestosis and/or lung cancer. The latency period for these disorders is at least 20 years, so men and women who mined the mineral or used it for various construction purposes during the 1940s and 1950s were not aware of their risk for these diseases until late in their lives. Today, uses of the mineral in which humans are likely to be exposed to its fibers have largely been discontinued.

Barite is the name given to a naturally occurring form of barium sulfate, commonly found in Canada, Mexico, and the states of Arkansas, Georgia, Missouri, and Nevada. One of the most important uses of barite is in the production of heavy muds that are used in drilling oil and gas wells. It is also used in the manufacture of a number of other commercially important industrial products such as paper coatings, battery plates, paints, linoleum and oilcloth, plastics, lithographic inks, and as filler in some kinds of textiles. Barium compounds are also widely used in medicine to provide the opacity that is needed in taking certain kinds of x rays.

Boron is a non-metallic element obtained most commonly from naturally occurring minerals known as borates. The borates contain oxygen, hydrogen, sodium, and other elements in addition to boron. Probably the most familiar boron-containing mineral is borax, mined extensively in salt lakes and alkaline soils.

Borax was known in the ancient world and used to make glazes and hard glass. Today, it is still an important ingredient of glassy products that include heat-resistant glass (Pyrex), glass wool and glass fiber, enamels, and other kinds of ceramic materials. Elementary boron also has a number of interesting uses. For example, it is used in nuclear reactors to absorb excess neutrons, in the manufacture of special-purpose alloys, in the production of semiconductors, and as a component or rocket propellants.

Corundum is a naturally occurring form of aluminum oxide that is found abundantly in Greece and Turkey and in New York State. It is a very hard mineral with a high melting point. It is relatively inert chemically and does not conduct an electrical current very well.

These properties make corundum highly desirable as a refractory (a substance capable of withstanding very high temperatures) and as an abrasive (a material used for cutting, grinding, and polishing other materials). One of the more mundane uses of corundum is in the preparation of toothpaste, where its abrasive properties help in keeping teeth clean and white.

In its granular form, corundum is known as emery. Many consumers are familiar with emery boards used for filing fingernails. Emery, like corundum, is also used in the manufacture of cutting, grinding, and polishing wheels.

The feldspars are a class of minerals known as the aluminum silicates. That is, they all contain aluminum, silicon, and oxygen, as sodium, potassium, and calcium. In many cases, the name feldspar is reserved for the potassium aluminum silicates. The most important commercial use of feldspar is in the manufacture of pottery, enamel, glass, and ceramic materials. The hardness of the mineral also makes it desirable as an abrasive.

Fluorspar is a form of calcium fluoride that occurs naturally in many parts of the world including North America, Mexico, and Europe. The compound gets its name from one of its oldest uses, as a flux. In Latin, the word fluor means flux. A flux is a material that is used in industry to assist in the mixing of other materials or to prevent the formation of oxides during the refining of a metal. For example, fluorspar is often added to an open-hearth steel furnace to react with any oxides that might form during that process. The mineral is also used during the smelting of an ore (the removal of a metal from its naturally occurring ore).

Fluorspar is also the principal source of fluorine gas. The mineral is first converted to hydrogen fluoride which, in turn, is then converted to the element fluorine. Some other uses of fluorspar are in the manufacture of paints and certain types of cement, in the production of emery wheels and carbon electrodes, and as a raw material for phosphors (a substance that glows when bombarded with energy, such as the materials used in color television screens).

The term phosphate refers to any chemical compound containing a characteristic grouping of atoms, given by the formula PO4, or comparable groupings. In the field of industrial minerals, the term most commonly refers to a specific naturally occurring phosphate, calcium phosphate, or phosphate rock. By far the most important use of phosphate rock is in agriculture, where it is treated to produce fertilizers and animal feeds. Typically, about 80% of all the phosphate rock used in the United States goes to one of these agricultural applications.

Phosphate rock is also an important source for the production of other phosphate compounds, such as sodium, potassium, and ammonium phosphate. Each of these compounds, in turn, has a very large variety of uses in everyday life. For example, one form of sodium phosphate is a common ingredient in dishwashing detergents. Another, ammonium phosphate, is used to treat cloth to make it fire retardant. Potassium phosphate is used in the preparation of baking powder.

As with other industrial minerals mentioned here, the term potassium salts applies to a large group of compounds, rather than one single compound. Potassium chloride, sulfate, and nitrate are only three of the most common potassium salts used in industry. The first of these, known as sylvite, can be obtained from salt water or from fossil salt beds. It makes up roughly 1% of each deposit, the remainder of the deposit being sodium chloride (halite).

Potassium salts are similar to phosphate rocks in that their primary use is in agriculture, where they are made into fertilizers, and in the chemical industry, where they are converted into other compounds of potassium. Some compounds of potassium have particularly interesting uses. Potassium nitrate, for example, is unstable and is used in the manufacture of explosives, fireworks, and matches.

Like potassium chloride, sodium chloride (halite) is found both in sea water and in underground salt mines left as the result of the evaporation of ancient seas. Sodium chloride has been known to and used by humans for thousands of years and is best known by its common name of salt, or table salt. By far its most important use is in the manufacture of other industrial chemicals, including sodium hydroxide, hydrochloric acid, chlorine, and metallic sodium. In addition, sodium chloride has many industrial and commercial uses. Among these are in the preservation of foods (by salting, pickling, corning, curing, or some other method), highway de-icing, as an additive for human and other animal foods, in the manufacture of glazes for ceramics, in water softening, and in the manufacture of rubber, metals, textiles, and other commercial products.

Sulfur occurs in its elementary form in large underground deposits from which it is obtained by traditional mining processes or, more commonly, by the Frasch process. In the Frasch process, superheated water is forced down a pipe that has been sunk into a sulfur deposit. The heated water melts the sulfur, which is then forced up a second pipe to the earth's surface.

The vast majority of sulfur is used to manufacture a single compound, sulfuric acid. Sulfuric acid consistently ranks number one in the United States as the chemical produced in largest quantity. Sulfuric acid has a very large number of uses, including the manufacture of fertilizers, the refining of petroleum, the pickling of steel (the removal of oxides from the metal's surface), and the preparation of detergents, explosives, and synthetic fibers.

A significant amount of sulfur is also used to produce sulfur dioxide gas (actually an intermediary in the manufacture of sulfuric acid). Sulfur dioxide, in turn, is extensively used in the pulp and paper industry, as a refrigerant, and in the purification of sugar and the bleaching of paper and other products. Some sulfur is refined after being mined and then used in its elemental form. This sulfur finds application in the vulcanization of rubber, as an insecticide or fungicide, and in the preparation of various chemicals and pharmaceuticals.

See also Geochemistry; Petroleum, economic uses of