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Minerals

Nutrition and Well-Being A to Z - Cite This Source

Minerals are inorganic elements that originate in the earth and cannot be made in the body. They play important roles in various bodily functions and are necessary to sustain life and maintain optimal health, and thus are essential nutrients. Most of the minerals in the human diet come directly from plants and water, or indirectly from animal foods. However, the mineral content of water and plant foods varies geographically because of variations in the mineral content of soil from region to region.

The amount of minerals present in the body, and their metabolic roles, varies considerably. Minerals provide structure to bones and teeth and participate in energy production, the building of protein, blood formation, and several other metabolic processes. Minerals are categorized into major and trace minerals, depending on the amount needed per day. Major minerals are those that are required in the amounts of 100 mg (milligrams) or more, while trace minerals are required in amounts less than 100 mg per day. The terms major and trace, however, do not reflect the importance of a mineral in maintaining health, as a deficiency of either can be harmful.

Some body processes require several minerals to work together. For example, calcium, magnesium, and phosphorus are all important for the formation and maintenance of healthy bones. Some minerals compete with each other for absorption, and they interact with other nutrients as well, which can affect their bioavailability.

Mineral Bioavailability

The degree to which the amount of an ingested nutrient is absorbed and available to the body is called bioavailability. Mineral bioavailability depends on several factors. Higher absorption occurs among individuals who are deficient in a mineral, while some elements in the diet (e.g., oxalic acid or oxalate in spinach) can decrease mineral availability by chemically binding to the mineral. In addition, excess intake of one mineral can influence the absorption and metabolism of other minerals. For example, the presence of a large amount of zinc in the diet decreases the absorption of iron and copper. On the other hand, the presence of vitamins in a meal enhances the absorption of minerals in the meal. For example, vitamin C improves iron absorption, and vitamin D aids in the absorption of calcium, phosphorous, and magnesium.

In general, minerals from animal sources are absorbed better than those from plant sources as minerals are present in forms that are readily absorbed and binders that inhibit absorption, such as phytates, are absent. Vegans (those who restrict their diets to plant foods) need to be aware of the factors affecting mineral bioavailability. Careful meal planning is necessary to include foods rich in minerals and absorption-enhancing factors.

Major Minerals

The major minerals present in the body include sodium, potassium, chloride, calcium, magnesium, phosphorus, and sulfur.

Functions.

The fluid balance in the body, vital for all life processes, is maintained largely by sodium, potassium, and chloride. Fluid balance is regulated by charged sodium and chloride ions in the extracellular fluid (outside the cell) and potassium in the intracellular fluid (inside the cell), and by some other electrolytes across cell membranes. Tight control is critical for normal muscle contraction, nerve impulse transmission, heart function, and blood pressure. Sodium plays an important role in the absorption of other nutrients, such as glucose, amino acids, and water. Chloride is a component of hydrochloric acid, an important part of gastric juice (an acidic liquid secreted by glands in the stomach lining) and aids in food digestion. Potassium and sodium act as cofactors for certain enzymes.

Calcium, magnesium, and phosphorus are known for their structural roles, as they are essential for the development and maintenance of bones and teeth. They are also needed for maintaining cell membranes and connective tissue. Several enzymes, hormones, and proteins that regulate energy and fat metabolism require calcium, magnesium and/or phosphorus to become active. Calcium also aids in blood clotting. Sulfur is a key component of various proteins and vitamins and participates in drug-detoxifying pathways in the body.

Disease prevention and treatment.

Sodium, chloride, and potassium are linked to high blood pressure (hypertension) due to their role in the body's fluid balance. High salt or sodium chloride intake has been linked to cardiovascular disease as well. High potassium intakes, on the other hand, have been associated with a lower risk of stroke, particularly in people with hypertension. Research also suggests a preventive role for magnesium in hypertension and cardiovascular disease, as well as a beneficial effect in the treatment of diabetes, osteoporosis, and migraine headaches.

Osteoporosis is a bone disorder in which bone strength is compromised, leading to an increased risk of fracture. Along with other lifestyle factors, intake of calcium and vitamin D plays an important role in the maintenance of bone health and the prevention and treatment of osteoporosis. Good calcium nutrition, along with low salt and high potassium intake, has been linked to prevention of hypertension and kidney stones.

Deficiency.

Dietary deficiency is unlikely for most major minerals, except in starving people or those with protein-energy malnutrition in developing countries, or people on poor diets for an extended period, such as those suffering from alcoholism, anorexia nervosa, or bulimia. Most people in the world consume a lot of salt, and it is recommended that they moderate their intake to prevent chronic diseases (high salt intake has been associated with an increased risk of death from stroke and cardiovascular disease). However, certain conditions, such as severe or prolonged vomiting or diarrhea, the use of diuretics, and some forms of kidney disease, lead to an increased loss of minerals, particularly sodium, chloride, potassium, and magnesium. Calcium intakes tend to be lower in women and vegans who do not consume dairy products. Elderly people with suboptimal diets are also at risk of mineral deficiencies because of decreased absorption and increased excretion of minerals in the urine.

Toxicity.

Toxicity from excessive dietary intake of major minerals rarely occurs in healthy individuals. Kidneys that are functioning normally can regulate mineral concentrations in the body by excreting the excess amounts in urine. Toxicity symptoms from excess intakes are more likely to appear with acute or chronic kidney failure.

Sodium and chloride toxicity can develop due to low intake or excess loss of water. Accumulation of excess potassium in plasma may result from the use of potassium-sparing diuretics (medications used to treat high blood pressure, which increase urine production, excreting sodium but not potassium), insufficient aldosterone secretion (a hormone that acts on the kidney to decrease sodium secretion and increase potassium secretion), or tissue damage (e.g., from severe burns). Magnesium intake from foods has no adverse effects, but a high intake from supplements when kidney function is limited increases the risk of toxicity. The most serious complication of potassium or magnesium toxicity is cardiac arrest. Adverse effects from excess calcium have been reported only with consumption of large quantities of supplements. Phosphate toxicity can occur due to absorption from phosphate salts taken by mouth or in enemas.

Trace Minerals

Trace minerals are present (and required) in very small amounts in the body. An understanding of the important roles and requirements of trace minerals in the human body is fairly recent, and research is still ongoing. The most important trace minerals are iron, zinc, copper, chromium, fluoride, iodine, selenium, manganese, and molybdenum. Some others, such as arsenic, boron, cobalt, nickel, silicon, and vanadium, are recognized as essential for some animals, while others, such as barium, bromine, cadmium, gold, silver, and aluminum, are found in the body, though little is known about their role in health.

Functions.

Trace minerals have specific biological functions. They are essential in the absorption and utilization of many nutrients and aid enzymes and hormones in activities that are vital to life. Iron plays a major role in oxygen transport and storage and is a component of hemoglobin in red blood cells and myoglobin in muscle cells. Cellular energy production requires many trace minerals, including iron, copper, and zinc, which act as enzyme cofactors in the synthesis of many proteins, hormones, neurotransmitters, and genetic material.

Iron and zinc support immune function, while chromium and zinc aid insulin action. Zinc is also essential for many other bodily functions, such as growth, development of sexual organs, and reproduction. Zinc, copper and selenium prevent oxidative damage to cells. Fluoride stabilizes bone mineral and hardens tooth enamel, thus increasing resistance to tooth decay. Iodine is essential for normal thyroid function, which is critical for many aspects of growth and development, particularly brain development. Thus, trace minerals contribute to physical growth and mental development.

Role in disease prevention and treatment.

In addition to clinical deficiency diseases such as anemia and goiter, research indicates that trace minerals play a role in the development, prevention, and treatment of chronic diseases. A marginal status of several trace minerals has been found to be associated with infectious diseases, disorders of the stomach, intestine, bone, heart, and liver, and cancer, although further research is necessary in many cases to understand the effect of supplementation. Iron, zinc, copper, and selenium have been associated with immune response conditions. Copper, chromium and selenium have been linked to the prevention of cardiovascular disease. Excess iron in the body, on the other hand, can increase the risk of cardiovascular disease, liver and colorectal cancer, and neurodegenerative diseases such as Alzheimer's disease. Chromium supplementation has been found to be beneficial in many studies of impaired glucose tolerance, a metabolic state between normal glucose regulation and diabetes. Fluoride has been known to prevent dental caries and osteoporosis, while potassium iodide supplements taken immediately before or after exposure to radiation can decrease the risk of radiation-induced thyroid cancer.

Deficiency.

With the exception of iron, dietary deficiencies are rare in the United States and other developed nations. However, malnutrition in developing countries increases the risk for trace-mineral deficiencies among children and other vulnerable groups. In overzealous supplement users, interactions among nutrients can inhibit absorption of some minerals leading to deficiencies. Patients on intravenous feedings without mineral supplements are at risk of developing deficiencies as well.

Although severe deficiencies of better-understood trace minerals are easy to recognize, diagnosis is difficult for less-understood minerals and for mild deficiencies. Even mild deficiencies of trace minerals however, can result in poor growth and development in children.

Iron deficiency is the most common nutrient deficiency worldwide, including in the United States. Iron-deficiency anemia affects hundreds of millions of people, with highest prevalence in developing countries. Infants, young children, adolescents, and pregnant and lactating women are especially vulnerable due to their high demand for iron. Menstruating women are also vulnerable due to blood loss. Vegetarians are another vulnerable group, as iron from plant foods is less bioavailable than that from animal sources.

Zinc deficiency, marked by severe growth retardation and arrested sexual development, was first reported in children and adolescent boys in Egypt, Iran, and Turkey. Diets in Middle Eastern countries are typically high in fiber and phytates, which inhibit zinc absorption. Mild zinc deficiency has been found in vulnerable groups in the United States. Copper deficiency is rare, but can be caused by excess zinc from supplementation.

Deficiencies of fluoride, iodine, and selenium mainly occur due to a low mineral content in either the water or soil in some areas of the world. Fluoride deficiency is marked by a high prevalence of dental caries and is common in geographic regions with low water-fluoride concentration, which has led to the fluoridation of water in the United States and many other parts of the world. Goiter and cretinism (a condition in which body growth and mental development are stunted) have been eliminated by iodization of salt in the United States, but still occur in parts of the world where salt manufacture and distribution are not regulated. Selenium deficiency due to low levels of the mineral in soil is found in northeast China, and it has been associated with Keshan disease, a heart disorder prevalent among people of that area.

Toxicity.

Trace minerals can be toxic at higher intakes, especially for those minerals whose absorption is not regulated in the body (e.g., selenium and iodine). Thus, it is important not to habitually exceed the recommended intake levels. Although toxicity from dietary sources is unlikely, certain genetic disorders can make people vulnerable to overloads from food or supplements. One such disorder, hereditary hemochromatosis, is characterized by iron deposition in the liver and other tissues due to increased intestinal iron absorption over many years.

Chronic exposure to trace minerals through cooking or storage containers can result in overloads of iron, zinc, and copper. Fluorosis, a discoloration of the teeth, has been reported in regions where the natural content of fluoride in drinking water is high. Inhalation of manganese dust over long periods of time has been found to cause brain damage among miners and steelworkers in many parts of the world.

In summary, minerals, both major and trace, play vital roles in human health, and care must be taken to obtain adequate intakes from a wide variety of whole foods. The most common result of deficiencies is poor growth and development in children. Minerals interact with each other and with other nutrients, and caution is required when using supplements, as excess intake of one mineral can lead to the deficiency of another nutrient.

SEE ALSO ANEMIA; BIOAVAILABILITY; CALCIUM; DIETARY SUPPLEMENTS; OSTEOPOROSIS; VITAMINS, FAT-SOLUBLE; VITAMINS, WATER-SOLUBLE.

Sunitha Jasti

Bibliography

Wardlaw, Gordon M. (1999). Perspectives in Nutrition, 4th edition. Boston: WCB McGraw-Hill.

Whitney, Eleanor N., and Rolfes, Sharon R. (1996). Understanding Nutrition, 7th edition. New York: West Publishing.

Internet Resources

The American Dietetic Association (2002). "Position of The American Dietetic Association: Food Fortification and Dietary Supplements." Available from <http://www.eatright.com>

The Linus Pauling Institute. "Minerals." Available from <http://osu.orst.edu/dept/lpi>

United States Department of Agriculture (2002). "Dietary Reference Intakes (DRI) and Recommended Dietary Allowances (RDA)." Available from <http://www.nal.usda.gov/fnic/>

Nutrition and Well-Being A to Z
Copyright © 1999 by The Gale Group.
Published by The Gale Group. All rights reserved, including the right of reproduction in whole or in part in any form.

Minerals

The Gale Encyclopedia of Children's Health: Infancy Through Adolescence - Cite This Source

Definition

Minerals are inorganic nutrients. That is, they are materials found in foods that are essential for growth and health and do not contain the element carbon. The minerals that are relevant to human nutrition are water, sodium, potassium, chloride, calcium, phosphate, sulfate, magnesium, iron, copper, zinc, manganese, iodine, selenium, and molybdenum. Cobalt is a required mineral for human health, but it is supplied by vitamin B12. There is some evidence that chromium, boron, and other inorganic elements play some part in human nutrition, but their role has not been proven.

Description

Minerals should be provided by a normal, healthy diet. In special cases, additional mineral supplements may be called for. Preterm (low birth weight) infants have special needs for calcium, phosphorus, and sodium, as well as extra needs for vitamin D. Iron supplements may also be recommended.

The amount of each mineral that is needed to support growth during infancy and childhood, to maintain body weight and health, and to facilitate pregnancy and lactation, are listed in a table called the Recommended Dietary Allowances (RDA). This table was compiled by the Food and Nutrition Board, a committee that serves the United States government. The values listed in the RDA indicate the daily amounts that are expected to maintain health throughout most of the general population. The actual levels of each inorganic nutrient required by any given individual is likely to be less than that stated by the RDA. The RDAs are all based on studies that provided the exact, minimal requirement of each mineral needed to maintain health. However, the RDA values are actually greater than the minimal requirement, as determined by studies on small groups of healthy human subjects, in order to accommodate the variability expected among the general population.

Because of differences in individual diets and individual needs, the decision regarding any child's need for supplements should be made by the parents after discussion with the pediatrician and, where appropriate, a nutritionist. Children on a well-balanced diet do not require supplements, while those who are picky eaters or who routinely eat a poor diet may benefit from supplementation.

Girls should get their calcium from foods, particularly dairy products, rather than supplements. Dairy products were associated with higher bone mineral density in the spine, while calcium supplements had no such benefit.

General use

The following discussion describes the role of the major minerals in human nutrition.

Iron is essential for the formation of hemoglobin, the chemical in the blood that carries oxygen to the cells. Low levels of iron cause anemia. In severe cases, the children become flabby, and they fail to grow normally. Milder cases of iron deficiency may not produce any physical symptoms, but children may learn at a slower pace than children with a proper amount of iron in their diet. The combination of rice, beans, and meat consumed with fresh citrus fruit provides an excellent source of absorbable iron. Iron supplements are suggested for children who cannot or will not follow a proper diet through the first two years of life.

Calcium is required for proper development of bones and teeth. It is also needed for proper muscle activity and blood clotting. Lack of calcium can cause rickets, a condition in which the bones are soft and develop in abnormal shapes. Calcium must be accompanied by vitamin D in order to have the proper effects. Foods rich in calcium include almonds, swiss cheese, collards, sardines and salmon with bones, spinach, ice cream, kale, beet greens, cheddar cheese, molasses, oysters, milk, and broccoli.

Zinc deficiency has been associated with reduced growth and mental retardation. The best foods for zinc are lamb, beef, leafy grains, root vegetables such as potatoes and carrots, shellfish, and organ meats such as liver or kidneys. While a high fiber diet is important for health, too much fiber can reduce the absorption of zinc and lead to a zinc deficiency.

Iodine is needed in the diet for proper thyroid function. The best source of iodine is fish, but table salt normally has iodine added to it, and even modest amounts of salt will meet the daily iodine requirements.

Fluoride is needed for strong teeth. In many areas, drinking water contains fluoride that meets all normal needs, but for children who do not drink water or drink filtered or bottled water, fluoride supplements may be useful. Fluoride supplements may be useful for infants and then may be discontinued as the child gets older and starts drinking water.

Magnesium is found in so many parts of the body that it is almost impossible to describe the effects of low magnesium levels. The most common problems are twitching, and, because of the need for magnesium in the parathyroid gland, soft bones even when calcium and vitamin D are adequate. Because magnesium is found in most foods, deficiency is usually associated with absorption problems and requires medical attention.

Copper is required for blood and nerve fiber development. It is found in liver, nuts, and seafood.

Phosporus is needed for energy production, metabolism, and healthy bone development. The best sources are milk, cheese, meats, whole grains, eggs, peas, and beans.

Potassium is needed for muscle contractions and nerve function. Good sources of potassium are orange juice, milk, cheese, whole grains, and vegetables.

Selenium is needed for proper thyroid function. It has also been associated with prevention of some types of cancer in adults. Selenium supplements are not normally required except in children with phenylketonuria receiving a low-protein diet, although it may sometimes be associated with thyroid problems. In these cases, medical care is required.

Precautions

Although the greatest nutritional concern is with inadequate levels of minerals, it is possible to take too much, particularly when people already eating a normally healthy diet take supplements. The daily intake of minerals should be reviewed to prevent adverse effects.

Excess calcium may lead to constipation and kidney problems. Too much zinc may lead to diarrhea, vomiting, and kidney and heart problems. Excess iron may cause problems of the stomach and digestive tract, liver problems, an increased risk of diabetes, and male sexual problems.

Side effects

When minerals are taken properly, they have no side effects.

Interactions

Minerals can interact with drugs and in excess with each other. Iron and calcium are known to bind to drugs of the tetracycline family and inactivate the antibiotic. The compound of calcium and tetracycline may also be absorbed into a child's teeth, causing discoloration.

Too much calcium in the diet may inhibit absorption of iron, magnesium, phosphorus, and zinc. Excess iron may reduce the absorption of zinc.

Parental concerns

Following a proper balanced diet is the best prevention of both mineral deficiency and mineral overdose. Since many children and adolescents cannot or will not eat a balanced diet, the possible need for supplements should be discussed with an appropriate professional.

Many children fail to follow a proper diet. This may be because of excess intake of fast foods and snack foods of low nutritional value. It is important for parents to teach children the benefits of proper nutrition and the importance of maintaining a healthful diet.

At the same time, adolescents, particularly those who engage in sports, may feel that they will do better with increased levels of nutrients. Because of the risk of toxic reactions to minerals and some vitamins, children should be discouraged from taking vitamin supplements unless there is clear evidence of increased need.

Resources

BOOKS

Siberry, George K., and Robert Iannone, eds. The Harriett Lane Handbook, 15th ed. St. Louis, MO: Mosby, 2000.

PERIODICALS

Chanoine, J. P. "Selenium and thyroid function in infants, children, and adolescents." Biofactors 19 (2003): 137–43.

Matkovic, V., et al. "Nutrition influences skeletal development from childhood to adulthood: a study of hip, spine, and forearm in adolescent females." Journal of Nutrition 134 (March 2004): 701S–5S.

ORGANIZATIONS

American Dietetic Association. 120 South Riverside Plaza, Suite 2000, Chicago, IL 60606–6995. Web site: <www.eatright.org>.

Tom Brody, PhD Samuel Uretsky, PharmD

The Gale Encyclopedia of Children's Health: Infancy Through Adolescence
Copyright © 1999 by The Gale Group.
Published by The Gale Group. All rights reserved, including the right of reproduction in whole or in part in any form.

Mineral

Wikipedia, the free encyclopedia - Cite This Source

A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties. A rock, by comparison, is an aggregate of minerals and need not have a specific chemical composition. Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms. The study of minerals is called mineralogy.

Mineral definition and classification

To be classified as a true mineral, a substance must be a solid and have a crystalline structure. It must also be a naturally occurring, homogeneous substance with a defined chemical composition. Traditional definitions excluded organically derived material. However, the International Mineralogical Association in 1995 adopted a new definition:
a mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes.
The modern classifications include an organic class - in both the new Dana and the Strunz classification schemes.

The chemical composition may vary between end members of a mineral system. For example the plagioclase feldspars comprise a continuous series from sodium-rich albite (NaAlSi3O8) to calcium-rich anorthite (CaAl2Si2O8) with four recognized intermediate compositions between. Mineral-like substances that don't strictly meet the definition are sometimes classified as mineraloids. Other natural-occurring substances are nonminerals. Industrial minerals is a market term and refers to commercially valuable mined materials (see also Minerals and Rocks section below).

A crystal structure is the orderly geometric spatial arrangement of atoms in the internal structure of a mineral. There are 14 basic crystal lattice arrangements of atoms in three dimensions, and these are referred to as the 14 "Bravais lattices". Each of these lattices can be classified into one of the six crystal systems, and all crystal structures currently recognized fit in one Bravais lattice and one crystal system. This crystal structure is based on regular internal atomic or ionic arrangement that is often expressed in the geometric form that the crystal takes. Even when the mineral grains are too small to see or are irregularly shaped, the underlying crystal structure is always periodic, and can be determined by X-ray diffraction.

Chemistry and crystal structure together define a mineral. In fact, two or more minerals may have the same chemical composition, but differ in crystal structure (these are known as polymorphs). For example, pyrite and marcasite are both iron sulfide, but their arrangement of atoms differs. Similarly, some minerals have different chemical compositions, but the same crystal structure: for example, halite (made from sodium and chlorine), galena (made from lead and sulfur) and periclase (made from magnesium and oxygen) all share the same cubic crystal structure.

Crystal structure greatly influences a mineral's physical properties. For example, though diamond and graphite have the same composition (both are pure carbon), graphite is very soft, while diamond is the hardest of all known minerals. This happens because the carbon atoms in graphite are arranged into sheets which can slide easily past each other, while the carbon atoms in diamond form a strong, interlocking three-dimensional network.

There are currently more than 4,000 known minerals, according to the International Mineralogical Association, which is responsible for the approval of and naming of new mineral species found in nature. Of these, perhaps 150 can be called "common," 50 are "occasional," and the rest are "rare" to "extremely rare."

Differences between minerals and rocks

A mineral is a naturally occurring, inorganic solid with a definite chemical composition and a specific crystalline structure. A rock is an aggregate of one or more minerals. (A rock may also include organic remains and mineraloids.) Some rocks are predominantly composed of just one mineral. For example, limestone is a sedimentary rock composed almost entirely of the mineral calcite. Other rocks contain many minerals, and the specific minerals in a rock can vary widely. Some minerals, like quartz, mica or feldspar are common, while others have been found in only one or two locations worldwide. The vast majority of the rocks of the Earth's crust consist of quartz, feldspar, mica, chlorite, kaolin, calcite, epidote, olivine, augite, hornblende, magnetite, hematite, limonite and a few other minerals. Over half of the mineral species known are so rare that they have only been found in a handful of samples, and many are known from only one or two small grains.

Commercially valuable minerals and rocks are referred to as industrial minerals. Rocks from which minerals are mined for economic purposes are referred to as ores (the rocks and minerals that remain, after the desired mineral has been separated from the ore, are referred to as tailings).

Mineral composition of rocks

A main determining factor in the formation of minerals in a rock mass is the chemical composition of the mass, for a certain mineral can be formed only when the necessary elements are present in the rock. Calcite is most common in limestones, as these consist essentially of calcium carbonate; quartz is common in sandstones and in certain igneous rocks which contain a high percentage of silica.

Other factors are of equal importance in determining the natural association or paragenesis of rock-forming minerals, principally the mode of origin of the rock and the stages through which it has passed in attaining its present condition. Two rock masses may have very much the same bulk composition and yet consist of entirely different assemblages of minerals. The tendency is always for those compounds to be formed which are stable under the conditions under which the rock mass originated. A granite arises by the consolidation of a molten magma at high temperatures and great pressures and its component minerals are those stable under such conditions. Exposed to moisture, carbonic acid and other subaerial agents at the ordinary temperatures of the Earth's surface, some of these original minerals, such as quartz and white mica are relatively stable and remain unaffected; others weather or decay and are replaced by new combinations. The feldspar passes into kaolinite, muscovite and quartz, and any mafic minerals such as pyroxenes, amphiboles or biotite have been present they are often altered to chlorite, epidote, rutile and other substances. These changes are accompanied by disintegration, and the rock falls into a loose, incoherent, earthy mass which may be regarded as a sand or soil. The materials thus formed may be washed away and deposited as sandstone or siltstone. The structure of the original rock is now replaced by a new one; the mineralogical constitution is profoundly altered; but the bulk chemical composition may not be very different. The sedimentary rock may again undergo metamorphism. If penetrated by igneous rocks it may be recrystallized or, if subjected to enormous pressures with heat and movement during mountain building, it may be converted into a gneiss not very different in mineralogical composition though radically different in structure to the granite which was its original state.

Physical properties of minerals

Classifying minerals can range from simple to very difficult. A mineral can be identified by several physical properties, some of them being sufficient for full identification without equivocation. In other cases, minerals can only be classified by more complex chemical or X-ray diffraction analysis; these methods, however, can be costly and time-consuming.

Physical properties commonly used are:

  • Crystal structure and habit: See the above discussion of crystal structure. A mineral may show good crystal habit or form, or it may be massive, granular or compact with only microscopically visible crystals.

  • Hardness: the physical hardness of a mineral is usually measured according to the Mohs scale. This scale is relative and goes from 1 to 10. Minerals with a given Mohs hardness can scratch the surface of any mineral that has a lower hardness than itself.

    • Moh's Hardness scale:
  • Talc Mg3Si4O10(OH)2
  • Gypsum CaSO4·2H2O
  • Calcite CaCO3
  • Fluorite CaF2
  • Apatite Ca5(PO4)3(OH,Cl,F)
  • Orthoclase KAlSi3O8
  • Quartz SiO2
  • Topaz Al2SiO4(OH,F)2
  • Corundum Al2O3
  • Diamond C (pure carbon)

  • Luster indicates the way a mineral's surface interacts with light and can range from dull to glassy (vitreous).

    • Metallic -high reflectivity like metal: galena and pyrite
    • Sub-metallic -slightly less than metallic reflectivity: magnetite
    • Non-metallic lusters:

      • Adamantine - brilliant, the luster of diamond also cerussite and anglesite
      • Vitreous -the luster of a broken glass: quartz
      • Pearly - iridescent and pearl-like: talc and apophyllite
      • Resinous - the luster of resin: sphalerite and sulfur
      • Silky - a soft light shown by fibrous materials: gypsum and chrysotile
      • Dull/earthy -shown by finely crystallized minerals: the kidney ore variety of hematite

  • Color indicates the appearance of the mineral in reflected light or transmitted light for translucent minerals (i.e. what it looks like to the naked eye).

    • Iridescence - the play of colors due to surface or internal interference. Labradorite exhibits internal iridescence whereas hematite and sphalerite often show the surface effect.
  • Streak refers to the color of the powder a mineral leaves after rubbing it on an unglazed porcelain streak plate. Note that this is not always the same color as the original mineral.
  • Cleavage describes the way a mineral may split apart along various planes. In thin sections, cleavage is visible as thin parallel lines across a mineral.
  • Fracture describes how a mineral breaks when broken contrary to its natural cleavage planes.

    • Chonchoidal fracture is a smooth curved fracture with concentric ridges of the type shown by glass.
    • Hackley is jagged fracture with sharp edges.
    • Fibrous
    • Irregular
  • Specific gravity relates the mineral mass to the mass of an equal volume of water, namely the density of the material. While most minerals, including all the common rock-forming minerals, have a specific gravity of 2.5 - 3.5, a few are noticeably more or less dense, e.g. several sulfide minerals have high specific gravity compared to the common rock-forming minerals.
  • Other properties: fluorescence (response to ultraviolet light), magnetism, radioactivity, tenacity (response to mechanical induced changes of shape or form), piezoelectricity and reactivity to dilute acids.

Chemical properties of minerals

Minerals may be classified according to chemical composition. They are here categorized by anion group. The list below is in approximate order of their abundance in the Earth's crust. The list follows the Dana classification system.

Silicate class

The largest group of minerals by far are the silicates (most rocks are ≥95% silicates), which are composed largely of silicon and oxygen, with the addition of ions such as aluminium, magnesium, iron, and calcium. Some important rock-forming silicates include the feldspars, quartz, olivines, pyroxenes, amphiboles, garnets, and micas.

Carbonate class

The carbonate minerals consist of those minerals containing the anion (CO3)2- and include calcite and aragonite (both calcium carbonate), dolomite (magnesium/calcium carbonate) and siderite (iron carbonate). Carbonates are commonly deposited in marine settings when the shells of dead planktonic life settle and accumulate on the sea floor. Carbonates are also found in evaporitic settings (e.g. the Great Salt Lake, Utah) and also in karst regions, where the dissolution and reprecipitation of carbonates leads to the formation of caves, stalactites and stalagmites. The carbonate class also includes the nitrate and borate minerals.

Sulfate class

Sulfates all contain the sulfate anion, SO42-. Sulfates commonly form in evaporitic settings where highly saline waters slowly evaporate, allowing the formation of both sulfates and halides at the water-sediment interface. Sulfates also occur in hydrothermal vein systems as gangue minerals along with sulfide ore minerals. Another occurrence is as secondary oxidation products of original sulfide minerals. Common sulfates include anhydrite (calcium sulfate), celestine (strontium sulfate), barite (barium sulfate), and gypsum (hydrated calcium sulfate). The sulfate class also includes the chromate, molybdate, selenate, sulfite, tellurate, and tungstate minerals.

Halide class

The halides are the group of minerals forming the natural salts and include fluorite (calcium fluoride), halite (sodium chloride), sylvite (potassium chloride), and sal ammoniac (ammonium chloride). Halides, like sulfates, are commonly found in evaporitic settings such as playa lakes and landlocked seas such as the Dead Sea and Great Salt Lake. The halide class includes the fluoride, chloride, bromide and iodide minerals.

Oxide class

Oxides are extremely important in mining as they form many of the ores from which valuable metals can be extracted. They also carry the best record of changes in the Earth's magnetic field. They commonly occur as precipitates close to the Earth's surface, oxidation products of other minerals in the near surface weathering zone, and as accessory minerals in igneous rocks of the crust and mantle. Common oxides include hematite (iron oxide), magnetite (iron oxide), chromite (iron chromium oxide), spinel (magnesium aluminium oxide - a common component of the mantle), ilmenite (iron titanium oxide), rutile (titanium dioxide), and ice (hydrogen oxide). The oxide class includes the oxide and the hydroxide minerals.

Sulfide class

Many sulfide minerals are economically important as metal ores. Common sulfides include pyrite (iron sulfide - commonly known as fools' gold), chalcopyrite (copper iron sulfide), pentlandite (nickel iron sulfide), and galena (lead sulfide). The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, and the sulfosalts (sulfur and a second anion such as arsenic).

Phosphate class

The phosphate mineral group actually includes any mineral with a tetrahedral unit AO4 where A can be phosphorus, antimony, arsenic or vanadium. By far the most common phosphate is apatite which is an important biological mineral found in teeth and bones of many animals. The phosphate class includes the phosphate, arsenate, vanadate, and antimonate minerals.

Element class

The elemental group includes metals and intermetallic elements (gold, silver, copper), semi-metals and non-metals (antimony, bismuth, graphite, sulfur). This group also includes natural alloys, such as electrum (a natural alloy of gold and silver), phosphides, silicides, nitrides and carbides (which are usually only found naturally in a few rare meteorites).

Organic class

The organic mineral class includes biogenic substances in which geological processes have been a part of the genesis or origin of the existing compound. Minerals of the organic class include various oxalates, mellitates, citrates, cyanates, acetates, formates, hydrocarbons and other miscellaneous species. Examples include whewellite, moolooite, mellite, fichtelite, carpathite, evenkite and abelsonite.

See also

External links

References

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Last updated on Thursday March 13, 2008 at 08:14:21 PDT (GMT -0700)
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