Products of Weathering

DATE:____________________________

ENVIRONMENTAL EARTH SCIENCE

PRODUCTS OF WEATHERING EXERCISE

INSTRUCTIONS: Read the following paragraphs then answer the questions at the end of each paragraph. Use a dictionary or your text to look up any unfamiliar words (except the names of the clays).

The end products of the weathering process may be of economic significance. One of the most common end products of weathering is bauxite, the primary ore of aluminum. The main type of bauxite result from weathering of aluminum-rich rocks and clays in subtropical to tropical climates. Bauxite is mined in many tropical or subtropical areas such as northern Australia, Jamaica, Brazil, Guinea, Suriname, and Central Africa.

1. Why is bauxite important?

2. How does bauxite form?

3. Name five minerals that weather to form bauxite (use your textbook).

4. Why doesn't bauxite form in the U.S. ?

5. How can recycling aluminum help the U.S. economy?

CLAYS

A common weathering product is kaolin, a fine clay which is used as a white pigment. The largest user of kaolin is the paper industry, which utilizes it as a filler and as a coating material to give paper a good printing surface for color. Kaolin is also used as a filler for rubber, paint, and plastics and as an absorbent in medicine.

6. What is a pigment?

7. What industry uses the most kaolin?

8. How can clay be used as a filler?

9. Why do you think high quality dishes are called china?

Ball clays are usually much darker because they contain more organic material, but they fire to a light cream to white color. For these reasons, ball clays are used extensively in ceramics in whitewares (like dishes), sanitary ware (like sinks), and wall tile, and as suspending agents in glazes and porcelain enamels.

10. Name five ceramic things that you have used over the past day that may have been made from ball clays.

Fireclays are soft, plastic clays used primarily in making refractory materials that will withstand temperatures of 1,500 oC or more.

11. What in your house may contain firebrick made from this type of clay?

Bentonite is an important industrial clay formed by the weathering of volcanic ash. One of its most important uses is as drilling mud in the petroleum industry--it removes drill cuttings from the hole, forms a filter cake on the wall of the hole to prevent drilling fluid loss and keep groundwater from entering, cools and lubricates the bit, and keeps barite (a weighting agent) in suspension in order to prevent blowouts.

12. If Bentonite clay were to become scarce, how would this affect the price of gasoline?

Bentonite clays are also used as bonding clays in foundries; as bonding agents for taconite and iron ore pellets; as adsorbents; as decolorizers for fats and oils; and as liners for ditches and ponds to prevent water loss. In addition to fine particle size, bentonites have the unique capability of swelling when they become wet.

13. What do you think a bonding agent does?

14. What do you think an oil decolorizer does?

15. If Bentonite clay were to become scarce, how would this affect the price of food that is grown with water from artificial ponds and ditches?

16. How could you use Bentonite clay to stop leaks from a reservoir?

Another clay, called attapulgite, is mined in northern Florida and southwestern Georgia and is used as a saltwater drilling mud; in adhesives to control viscosity; as a thickener in latex paints, liquid suspension fertilizers, and pharmaceuticals; and as pet litter, oil adsorbent, carriers for agricultural chemicals, flatting agent in paint, and anticaking agent.

17. How have you used attapulgite indirectly?

By far the largest use for the other clays is in the manufacture of structural clay products--brick, sewer pipe, drain tile, conduit tile, glazed floor tile, terra-cotta, and red pottery--and for the production of lightweight aggregate, an additive for mortars, cements, and concretes with good structural properties and high crushing strengths.

18. List five places you have been where these structural clays are used.

Other weathering products of economic importance include iron ore, manganese ore, titanium ores, phosphates, and uranium and vanadium minerals.

MATCHING

These resources: Are used for:

A. iron, manganese, _____ power generation

titanium, vanadium

B. phosphates _____ steel and metal industry

C. uranium _____ fertilizers

ENVIRONMENTAL EARTH SCIENCE PRODUCTS OF WEATHERING EXERCISE

ANSWERS

Why is bauxite important?

BAUXITE IS THE PRIMARY ORE OF ALUMINUM, WHICH IS USED TO MAKE A HUGE NUMBER OF THINGS.

How does bauxite form?

WEATHERING OF ALUMINUM-RICH ROCKS AND CLAYS IN WARM, WET CLIMATES.

Name five minerals that weather to form bauxite (use your textbook).

STANDARD TEXT: KAOLINITE, MUSCOVITE, BIOTITE, HORNBLENDE, FELDSPAR, AUGITE, GARNET, TOPAZ, CORUNDUM.

HONORS TEXT: CORUNDUM, GARNET, AUGITE, FELDSPAR, FIND KAOLINITE LATER IN WORKSHEET READING.

Why doesn't bauxite form in the U.S. ?

WE DO NOT HAVE A TROPICAL CLIMATE.

How can recycling aluminum help the U.S. economy?

BAUXITE OR ALUMINUM MUST BE IMPORTED INTO THE US, SO THE MORE ALUMINUM WE RECYCLE HERE, THE LESS ALUMINUM HAS TO BE BOUGHT FROM OTHER COUNTRIES.

What is a pigment?

COLORING MATTER USED TO MAKE PAINT.

What industry uses the most kaolin?

THE PAPER INDUSTRY.

How can clay be used as a filler?

IT FILLS IN HOLES AND LOW SPOTS IN THE PAPER.

Why do you think high quality dishes are called china?

THE FIRST MAJOR DEPOSIT OF KAOLINITE USED TO MAKE DISHES WAS FIRST FOUND IN CHINA.

Name five ceramic things that you have used over the past day that may have been made from ball clays.

CERAMIC CUP, SINKS, FLOOR AND WALL TILE, TOILET, TRIVET, CERAMIC SURFACES OF STOVES, APPLIANCES,

What in your house may contain firebrick made from this type of clay?

FURNACE FIREBOX, CHIMNEY LINING, FIREPLACE LINING, WOODSTOVE BRICKS.

If Bentonite clay were to become scarce, how would this affect the price of gasoline?

GAS PRICES WOULD GO UP BECAUSE DRILLING FOR OIL WOULD BE MORE DIFFICULT.

What do you think a bonding agent does?

HELPS MATERIAL LIKE IRON ORE TO STICK TOGETHER.

What do you think a decolorizer does?

TAKES AWAY COLOR.

If Bentonite clay were to become scarce, how would this affect the price of food that is grown with water from artificial ponds and ditches?

THE PRICE OF FOOD WOULD RISE BECAUSE FARMERS WOULD NOT BE ABLE TO BUILD AS MANY PONDS AND DITCHES FOR IRRIGATION, SO LESS FOOD WOULD BE GROWN.

How could you use Bentonite clay to stop leaks from a reservoir?

COAT THE RESEVOIR WALLS WITH IT OR PUSH IT INTO HOLES- AS IT GETS WET, IT EXPANDS AND PLUGS THE LEAK.

How have you used attapulgite indirectly?

ADHESIVES, LATEX PAINTS, FERTILIZER, PHARMECEUTICALS (MEDICINE), PET LITTER, OIL SPILLS IN THE GARAGE, EATING FOOD SPRAYED WITH AGRICULTURAL CHEMICALS, PAINT.

List five places you have been where these structural clays are used.

ANYWHERE WHERE THERE ARE BRICKS, SEWER OR SEPTIC SYSTEM PIPES, FLOOR TILES, FLOWER POTS, CLAY PATIO BLOCKS, TILE ROOFS, CLAY DRAIN PIPES.

MATCHING

These resources: Are used for:

A. iron, manganese, __C__ power generation

titanium, vanadium

B. phosphates __A__ steel and metal industry

C. uranium __B__ fertilizers

More info:

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The Academic American Encyclopedia, electronic version, Grolier Electronic Publishing, Danbury, Connecticut, 1991. Downloaded from GEnie 3/28/93.

------------------------------------------------------------------------Grolier 0309190-0 9104

weathering

Weathering has been defined in several ways; in simplest terms it is the rock breakdown, decomposition, and rotting that take place at or near the surface of the Earth. Weathering involves both physical and chemical reactions and is therefore dependent on such factors as climate, topography, vegetation, time, and the composition and texture of the parent rock.

Temperature and rainfall are significant climatic factors; rock decay is most rapid in warm, humid climates. Both the direction of water movement through the rocks and the leaching of soluble components depend on the amount of rainfall and its seasonal distribution. In a continuously wet climate water moves downward; in a dry climate the prevailing water movement may be upward, and the decay components may not be removed from the weathering zone.

Topography controls the vertical movement of groundwater, the rate of erosion, and the rate of removal of weathering products. In low, flat areas there is little movement of water through the soils and rocks and therefore relatively little leaching.

Vegetation is important because the products of organic decay, particularly in cool, humid climates where abundant organic acids can be produced, greatly affect the alteration process. The type of vegetation--that is, trees, grasses, and other plants--has drastic effects on the decomposition of the parent minerals and the resultant decomposition products.

Time is a significant factor in the development of weathering products because weathering processes are relatively slow. In the initial stages of weathering certain reactions may take place that are very different from subsequent reactions after the more soluble components are removed.

The most important chemical reactions that take place in weathering are hydrolysis, ion exchange, oxidation, carbonation, solution, and chemical reconstitution. Hydrolysis refers to the reaction between water and the rock or mineral. Ion exchange involves the chemical substitution of hydrogen ions for metallic cations. Oxidation, in the process of weathering, usually occurs by the combination of elemental oxygen with the atoms or ions in the rock or mineral. Carbonation is the combination of carbonate or bicarbonate with certain rock elements such as calcium, magnesium, and iron. Solution is the removal and transportation of ions, such as those of sodium and calcium, by water.

PRODUCTS OF WEATHERING

The end products of the weathering process may be of economic significance. One of the most common end products of weathering is bauxite, a rock comprised primarily of hydrated aluminum oxides. Bauxite is the primary ore of aluminum and is mined in many tropical or subtropical areas such as northern Australia, Jamaica, Brazil, Suriname, and Central Africa. Another common weathering product is kaolin, a fine clay (hydrated alumina silicate), which is used as a white pigment. The largest user of kaolin is the paper industry, which utilizes it as a filler and as a coating material to give paper a good printing surface for color. Kaolin is also used as a filler for rubber, paint, and plastics and as an absorbent in medicine.

Other weathering products of economic importance include iron ore, manganese ore, titanium ores, phosphates, and uranium and vanadium minerals. HAYDN H. MURRAY

Bibliography: Keller, Walter D., The Principles of Chemical Weathering, rev. ed. (1959); Loughnan, Fred C., Chemical Weathering of the Silicate Minerals (1969); Ollier, C. D., Weathering, rev. ed. (1975).

Grolier 0027500-0 9106

bauxite

{bawks'-yt}

Bauxite, the principal ore of aluminum, is a rock mixture consisting mostly of several hydrous aluminum oxide minerals, including boehmite; diaspore; gibbsite; and impurities such as QUARTZ, CLAY MINERALS, and iron hydroxides.

The nature of the rock makes the individual minerals difficult to distinguish. Boehmite occurs in microscopic plates (ORTHORHOMBIC SYSTEM) as well as in pea-shaped aggregates called pisolites. Diaspore, identical in chemical composition with boehmite but structured differently, occurs in EMERY deposits and in bauxite and LATERITE. It forms thin whitish, grayish, or colorless platy or elongated crystals, as well as scales and cleavable, foliated masses. Its HARDNESS is 6.5-7, its LUSTER is brilliant or vitreous pearly, and its SPECIFIC GRAVITY is 3.3-3.5. Gibbsite forms white or gray six-sided tabular crystals (MONOCLINIC SYSTEM) with one perfect cleavage. Often the chief mineral of bauxite or laterite deposits, it also occurs in low-temperature hydrothermal veins. Its hardness is 2.5 to 3.5, its luster is pearly or vitreous, and its specific gravity is 2.3 to 2.4.

Laterite, the principal type of bauxite deposit, contains pisolites ranging in size from that of buckshot up to 25 cm (10 in) in diameter. A mottled material that is white or gray when pure, it is colored pink, yellow, red, or brown by small amounts of iron. Lateritic bauxites result from WEATHERING of aluminum-rich rocks and clays in subtropical to TROPICAL CLIMATES. The world's leading producers of bauxite are Guinea, Australia, Jamaica, and Brazil.

Kaolin Clays

Several clays in commercial use consist largely of kaolinite, a hydrated aluminum silicate. Large deposits of this mineral occur in China; Czechoslovakia; Cornwall, England; and several states of the United States. Various grades of kaolin clays may be distinguished. White kaolin clays are fine in particle size, soft, nonabrasive, and chemically inert over a wide pH range. Their largest consumer is the paper industry, which uses them as a coating to make PAPER smoother, whiter, and more printable, and as a filler to enhance opacity and ink receptivity. Ball clays are usually much darker because they contain more organic carbonaceous material. These fine-grained refractory bond clays have excellent plasticity and strength, and they fire to a light cream to white color. For these reasons, ball clays are used extensively in CERAMICS in whitewares, sanitary ware, and wall tile, and as suspending agents in glazes and porcelain enamels.

Fireclays are soft, plastic clays used primarily in making REFRACTORY MATERIALS that will withstand temperatures of 1,500 degrees C or more. The most common fireclays, underclays, occur directly under coal seams.

Bentonites

Bentonite, an important industrial clay, is made up mainly of the mineral smectite (montmorillonite) and formed by the alteration of volcanic ash. One of its most important uses is as DRILLING mud in the petroleum industry--it removes drill cuttings from the hole, forms a filter cake on the wall of the hole to prevent drilling fluid loss and keep groundwater from entering, cools and lubricates the bit, and keeps barite (a weighting agent) in suspension in order to prevent blowouts.

Bentonites are also used as bonding clays in foundries; as bonding agents for taconite and iron ore pellets; as adsorbents; as decolorizers for fats and oils; and as liners for ditches and ponds to prevent water loss. In addition to fine particle size, bentonites have the unique capability of swelling when they become wet.

Other Varieties

Some clays--the hydrated magnesium aluminum silicates--consist of long, tubular particles. One such clay, attapulgite, is mined in northern Florida and southwestern Georgia. It is used as a saltwater drilling mud; in adhesives to control viscosity; as a thickener in latex paints, liquid suspension fertilizers, and pharmaceuticals; and as pet litter, oil adsorbent, carriers for agricultural chemicals, flatting agent in paint, and anticaking agent. Another variety, sepiolite, has nearly the same physical properties as attapulgite, but a higher aluminum and iron content. It is mined in the Amargosa Valley in Nevada.

Most other clays consist of mixtures of illite (a hydrated potassium-iron-aluminum silicate), CHLORITE, kaolinite, and smectite. By far the largest use for these miscellaneous clays is in the manufacture of structural clay products--brick, sewer pipe, drain tile, conduit tile, glazed floor tile, terra-cotta, and red pottery--and for the production of lightweight aggregate, an additive for mortars, cements, and concretes with good structural properties and high crushing strengths. These clays vary widely in physical properties, depending on composition and the particle size of the mineral constituents. The properties that are most important are plasticity, green (prefiring) strength, dry strength, drying and firing shrinkage, vitrification range, and fired color. The cement industry also uses clay, mostly as a source of aluminum and silica for the charge that is added to cement kilns. HADYN H. MURRAY

Bibliography: Bennett, Richard, and Hulbert, M. H., Clay Microstructure (1986); Fowden, Leslie, et al., eds., Clay Minerals: Their Structure, Behavior and Use (1984); Gillott, J. E., Clay in Engineering Geology, 2d ed. (1987); Grim, Ralph E., Clay Mineralogy, 2d ed. (1968); Grimshaw, R. W., The Chemistry and Physics of Clays and Other Ceramic Materials, 4th ed. (1971); Millot, G., Geology of Clays (1970); Newman, A. C., ed., Chemistry of Clays and Clay Minerals (1987); Picard, M. D., Grit and Clay (1975); Weaver, C. E., and Pollard, L. D., The Chemistry of Clay Minerals (1975); Worrall, W. E., Clays and Ceramic Raw Materials, 2d ed. (1986).

uranium minerals.

Principal Ore Minerals

The mineralogy and occurrence of uranium are controlled by its geochemical behavior. In igneous rocks it exists in the +4 valence state. This large ion tends to be excluded from early crystallizing ferromagnesian minerals, thus becoming more concentrated in residual liquids during the final stages of crystallization. In intermediate and granitic rocks it typically substitutes for calcium in apatite and for zirconium in zircon, and uranium concentration generally correlates with the silica content of igneous rocks. Most uranium in igneous rocks, however, is believed to exist in amorphous intergranular films.

Primary uranium minerals occur in some pegmatites and in high-temperature hydrothermal veins. These unoxidized black ores are typically uraninite (pitchblende), as in the Jachymov locality, but may include brannerite, coffinite, or davidite. Vein deposits have been mined in Zaire (formerly Belgian Congo); in the Northwest Territories, Saskatchewan, and Ontario in Canada; in the Northern Territory in Australia; in France; and in Colorado, Utah, and Alaska.

When exposed to more oxidizing conditions near the Earth's surface, these minerals and the intergranular phases in igneous rocks are readily oxidized to the highly soluble +6 valence state, and uranium is mobilized in surface water and groundwater. Geologists theorize that in the oxygen-free atmosphere of early Precambrian time (more than 2.3 billion years ago) oxidation did not occur, and uraninite and brannerite grains accumulated as detrital placer deposits in Precambrian quartz-pebble conglomerates. Large uranium resources of this type, which may also contain gold, are found in Canada, South Africa, and Brazil.

Much of the oxidized uranium in solution ultimately reaches the oceans. Although the uranium in seawater amounts to only 0.002 parts per million, it may be selectively removed and incorporated in marine phosphorite deposits, adsorbed by clay minerals, or incorporated in the carbonate skeletons of organisms such as corals. Marine phosphorites constitute large uranium resources in the United States, Africa, the USSR, Brazil, and the Mediterranean region. In Florida these low-grade deposits are extensively mined for their phosphate, which makes recovery of the uranium feasible. Some lignites and marine black shales also contain enough uranium to be considered resources.

More than 99 percent of the uranium now being mined in the United States comes from sedimentary deposits in New Mexico, Wyoming, Texas, Colorado, and Utah. These deposits apparently formed when uranium-bearing groundwater encountered chemically reducing conditions in sedimentary beds and precipitated reduced (+4) uranium minerals, principally uraninite and coffinite.

Oxidized uranium may also precipitate by interaction with primary vanadium minerals, forming the ore minerals carnotite and tyuyamunite. These deposits, typically tabular bodies enclosed in reduced sandstone and concordant with the sedimentary structure of the sandstone, represent a subsurface "wave" or moving interface between oxidizing and reducing conditions.