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A plant, Musa textilis, of the banana family that is valuable for its hard fiber (also known as Manila hemp). Abaca (Musa textilis) is a flowering plant native to the Philippines and Borneo. Taxonomically, it is assigned to the order Zingiberales.…

A variety of chalcedonic quartz that is distinguished by the presence of color banding in curved or irregular patterns (Fig. 1). Most agate used for ornamental purposes is composed of two or more tones or intensities of brownish-red, often…

A sodium-rich plagioclase feldspar mineral whose composition extends over the range Ab100An0 to Ab90An10, where Ab (= albite) is NaAlSi3O8 and An (= anorthite) is CaAl2Si2O8 (see illustration). Albite occurs in crustal igneous rocks as a major…

Most commonly, a generic name for all fossil resins, although it has been restricted by some to refer only to succinite, the mineralogical species of fossil resin that includes most of the Baltic Coast deposits. The time necessary to transform resin…

A lithium aluminum phosphate mineral of basic formula LiAl(PO4)(F). The structure of amblygonite consists of phosphate (PO4) groups of tetrahedra and AlO6 groups of octahedra. Each PO4 tetrahedron is connected to an AlO6 octahedron. Corner-sharing…

The transparent purple to violet variety of the mineral quartz. Although quartz is perhaps the commonest gem mineral known, amethyst (see illustration) is rare in the deep colors that characterize fine quality. Amethyst is usually colored unevenly…

A nesosilicate mineral, composition Al2SiO5, crystallizing in the orthorhombic system. Andalusite (Fig. 1) occurs commonly in large, nearly square prismatic crystals. The variety chiastolite has inclusions of dark-colored carbonaceous material…

A plagioclase feldspar with composition Ab70An30 to Ab50An50 (Ab = NaAlSi3O8; An = CaAl2Si2O8). Andesine (see illustration) occurs primarily in igneous rocks, often in a glassy matrix as small, chemically zoned, lathlike crystals known as…

A mineral with the chemical composition PbSO4. Anglesite occurs in white or gray, orthorhombic, tabular or prismatic crystals or compact masses (see illustration). It is a common secondary mineral, usually formed by the oxidation of galena. Fracture…

A mineral with the chemical composition CaSO4. Anhydrite (anhydrous calcium sulfate) occurs commonly in white and grayish granular masses, rarely in large, orthorhombic crystals (see illustration). Fracture is uneven and luster is pearly to…

The use of live nonhuman animals for scientific research and experimentation. Animal testing has been a cornerstone of biomedical research, having contributed greatly to the understanding of human biology, to the unraveling of the complex underlying…

The calcium-rich plagioclase feldspar with composition Ab0An100 to Ab10An90 (Ab = NaAlSi3O8; An = CaAl2Si2O8). Anorthite (see illustration) occurs in olivine-rich igneous rocks and rare volcanic ejecta (for example, at Mount Vesuvius, Italy, and…

The coldest, windiest, and driest continent. The lowest temperature ever measured on Earth, −89.2°C (−128.5°F), was recorded at the Russian Antarctic station of Vostok in July 1983. Katabatic (cold, gravitational) winds with velocities up to 50 km/h…

One of three naturally occurring mineral forms of calcium carbonate (CaCO3). The other forms (or polymorphs) are the abundant mineral calcite and the relatively rare mineral vaterite. Still other forms of calcium carbonate are known, but only as…

Arenite (rock composed of sand-size fragments) that contains a high proportion of feldspar in addition to quartz and other detrital minerals. Arkose is also known as feldspathic sandstone. Although there is no universal agreement, many geologists…

A group of monoclinic calcic pyroxenes which have the general chemical formula (Ca,Mg,Fe)(Mg,Fe)-Si2O6, in which calcium is the dominant cation in the first cation position. Monoclinic pyroxene with substantial iron or magnesium in place of calcium…

A basic carbonate of copper with the chemical formula Cu3(OH)2(CO3)2. Azurite is normally associated with copper ores and often occurs with malachite. Azurite is monoclinic. It may be massive or may occur in tabular, prismatic, or equant crystals…

A mineral with chemical composition BaSO4. It is isostructural with celestite, SrSO4, and anglesite, PbSO4. Barite is orthorhombic, space group Pnma, a = 0.887 nanometer, b = 0.545 nm, c = 0.714 nm. The illustration shows typical crystals. Barite…

The most common volcanic rock on Earth. Basalt is an igneous rock characterized by small grain size (less than about 5 mm) and approximately equal proportions of calcium-rich plagioclase feldspar and calcium-rich pyroxene, with less than about 20%…

The primary ore used to produce aluminum metal and alumina (Al2O3). Bauxite (see illustration) is a naturally occurring weathering product composed of one or more aluminum hydroxide minerals, such as gibbsite [Al(OH)3], boehmite [AlO(OH)], and…

Any of several leguminous plants, or their seeds, long utilized as food by humans or livestock. There are more than 40,000 varieties of beans, with only a small number of these being mass-produced for human or animal consumption. In particular,…

The most common beryllium mineral. Beryl, Al2[Be3Si6O18], crystallizes in the hexagonal system with space group P6/mcc. The crystal structure consists of six-membered rings of corner-sharing silicon-oxygen (SiO4) tetrahedra cross-linked by…

Minerals containing beryllium as an essential component. Over 50 beryllium minerals (Fig. 1) have been identified, even though beryllium is a scarce element in the Earth's crust. The unusual combination of low charge (+2) and small ionic radius…

An iron-magnesium-rich layer silicate; it is also known as black mica. Biotite (see illustration) is the most abundant of the mica group of minerals. The name is derived from that of the French chemist J. Biot. The formula for the ideal end member,…

A distinctive, fine-grained mudrock that derives its dark color from an unusually high content of organic matter, ranging from around 2% to over 50% of the weight of the rock (typical shales contain less than 1% organic matter). Most black shales…

Regional metamorphism with the highest pressures and lowest temperatures, commonly above 500 megapascals (5 kilobars) and below 400°C (750°F). Metamorphic rocks of the relatively uncommon blueschist facies contain assemblages of minerals that record…

A clastic rock composed of angular gravel-size fragments; the consolidated equivalent of rubble. The designation gravel-size refers to a mean particle diameter greater than 2 mm, which means that 50% or more of the particles (by volume) are this…

A mineral composed of calcium carbonate (CaCO3). Calcite is one of the most common minerals found in the Earth's crust. Calcite (Fig. 1) may be found in a great variety of sedimentary, metamorphic, and igneous rocks. It is also an important…

A type of carved gemstone in which the background is cut away to leave the subject in relief. Often cameos are cut from stones in which the coloring is layered, resulting in a figure of one color and a background of another. The term cameo (see…

A coarse, erect, annual herb plant, Ricinus communis, belonging to the spurge family (Euphorbiaceae). The castor plant (Ricinus communis) is a member of the spurge family (Euphorbiaceae) in the order Malpighiales. The plant varies greatly in height…

A mineral with the chemical composition SrSO4. Celestite occurs commonly in colorless to sky-blue, orthorhombic, tabular crystals (see illustration). Fracture is uneven and luster is vitreous. Hardness is 3–3.5 on Mohs scale and specific gravity is…

Any member of the grass family (Poaceae or Gramineae) that produces edible grains usable as food by humans and livestock. Cereals are important cultivated crops. Common cereals include rice, wheat, barley, oats, maize (corn), sorghum, rye, and…

A common mineral in the upper oxidized zone of ore deposits containing galena (PbS). Cerussite (see illustration) is usually associated with anglesite, smithsonite, malachite, and other secondary minerals. Normally cerussite is close in composition…

A mineral belonging to the zeolite family of silicates. Chabazite (see illustration) commonly occurs in well-crystallized groupings of crystals with external rhombohedral symmetry (point group 3 2/m) with nearly cubic angles. This well-developed…

A mineral with the chemical composition CuSO4· 5H2O. Chalcanthite commonly occurs in blue to greenish-blue triclinic crystals or in massive fibrous veins or stalactites (see illustration). Fracture is conchoidal and luster is vitreous. Hardness is…

A fine-grained fibrous variety of quartz, silicon dioxide. The individual fibers that compose the mineral aggregate usually are visible only under the microscope. Subvarieties of chalcedony recognized on the basis of color differences (induced by…

The term “chalk” is sometimes used in a broad sense for any soft, friable, or weathered fine-grained limestone; however the term is mostly restricted to pelagic (biogenic) limestones. Chalk is a uniformly fine-grained, typically light-colored marine…

A type of sweet or sour fruit of the Prunus genus, as well as the tree that bears the fruit. Cherry trees belong to the Prunus genus in the order Rosales, and the sweet and sour fruits of these trees are called cherries (Fig. 1). There are…

A hard, dense sedimentary rock composed of fine-grained silica (SiO2), most commonly quartz. Chert is characterized by a semivitreous to dull luster and a splintery to conchoidal fracture, and is most commonly gray, black, reddish brown, or green…

One of a group of layer silicate minerals, usually green in color, characterized by a perfect cleavage parallel to (001). Chlorite cleavage flakes are flexible but inelastic, with a luster varying from pearly or vitreous to dull and earthy. The…

A hydrous iron aluminum silicate mineral commonly found in low-grade metamorphic rocks such as slate and phyllite. Chloritoid is found as platy, black or dark green crystals, rarely more than a few millimeters in size (Fig. 1). Its density ranges…

A mineral having composition BeAl2O4 and crystallizing in the orthorhombic system. Chrysoberyl crystals (see illustration) are usually tabular parallel to the front pinacoid and frequently in pseudohexagonal twins. There is good prismatic cleavage.…

A silicate mineral with composition essentially (Cu,Al)2H2Si2O5(OH)4·nH2O; iron, and more rarely manganese, may substitute for copper. Although acicular monoclinic crystals have been reported, the wide variation in the composition of analyzed…

A fibrous asbestos mineral with a tubular morphology for each fibril. Chrysotile (Fig. 1) is a member of the serpentine mineral group, as are antigorite and lizardite. Chrysotile aggregates make up serpentine asbestos, which is the most common type…

An evergreen shrub or small tree, particularly Cinnamomum verum, and the spice obtained from the plant's bark. The cinnamon plant (see illustration) is a member of the laurel family (Lauraceae) in the order Laurales. Native to Sri Lanka, the…

Fine-grained, hydrous, layer silicates that belong to the larger class of sheet silicates known as phyllosilicates. Clay minerals form on Earth in many different environments, including the weathering environment, the sedimentary environment, and…

The long-term records of precipitation, temperature, wind, and all other aspects of the Earth's climate. Climate, like the Earth itself, has a history extending over several billion years. Climatic changes have occurred at time scales ranging from…

A loosely defined term used for a sedimentary mineral segregation that may range in size from millimeters to meters. Concretions (see illustration) are usually distinguished from the sedimentary matrix enclosing them by a difference in mineralogy,…

The consolidated equivalent of gravel. Conglomerates are aggregates of more or less rounded particles greater than 2 mm in diameter. Frequently they are divided on the basis of size of particles into pebble (fine), cobble (medium), and boulder…

The response of corals to environmental stress in which they eject the single-cell algae that live within the transparent coral tissue, making the white coral skeleton visible. Corals (Fig. 1) are animals that live in a partnership (symbiosis) with…

An orthorhombic magnesium aluminosilicate mineral of composition Mg2[Al4Si5O18], a = 1.710 nanometers, b = 0.973 nm, c = 0.936 nm, Z = 4, space group Cccm. The crystal structure is related to beryl; magnesium is octahedrally coordinated by oxygen…

A fiber obtained from the cotton plant Gossypium. The cotton plant (genus Gossypium, order Malvales; Fig. 1) has been used by humans for more than 5000 years. The fiber (cotton) obtained from this plant is the most widely used natural fiber because…

A mineral with chemical composition Na3AlF6. Although it crystallizes in the monoclinic system, cryolite has three directions of parting at nearly 90°, giving it a pseudocubic aspect. Hardness is 2½ on Mohs scale and the specific gravity is 2.95.…

Marine animal life inhabiting the portion of the oceans below the upper limit of the continental slopes. The marine animals that make up the deep-sea fauna live below the photic zone of the oceans. In general, the deep sea may be regarded as that…

The monoclinic pyroxene mineral which in pure form has the formula CaMgSi2O6. Diopside has no known polymorphs. Its structure consists of chains of SiO4 tetrahedrons in which each silicon ion shares an oxygen with each of its two nearest silicon…

A phaneritic (visibly crystallized) plutonic rock having intermediate SiO2 content (53–66%), composed mainly of plagioclase (oligoclase or andesine) and one or more ferromagnesian minerals (hornblende, biotite, or pyroxene), and having a granular…

A very dense rock composed of red-brown garnet and the grape-green pyroxene omphacite. Eclogites possess basaltic bulk chemistry, and their garnets are rich in the components pyrope (Mg3Al2Si3O12), almandine (Fe3Al2Si3O12), and grossular…

The biological study of insects that have a direct influence on humanity. Economic entomology is a subdiscipline of entomology (the biological science that deals with the investigation of insects) and focuses on the effects of insects on human…

The medium- to dark-green gem variety of the mineral beryl, Be3Al2Si6O18, crystallizing in the hexagonal system. A flawless emerald with good color is one of the most sought after and highly prized of all precious gems. Emerald is restricted in its…

The group name for a family of minerals of general composition Ca2(Fe3+, Al, Mn3+)Al2O[SiO4][Si2O]- (OH) which occur widely in metamorphic and igneous rocks (Fig. 1). Epidote [octahedral ferric iron (Fe3+) dominant] and clinozoisite [aluminum (Al)…

Any weather event that is unusual for a particular location or severe in its effects. The most commonly considered examples of extreme weather events include heat waves, cold snaps, heavy rainfall or snowfall, ice or hail storms, droughts,…

The segment of horticulture concerned with the commercial production, marketing, and sale of plants grown and used for decorative or display purposes. Floriculture is a branch of horticulture, that is, the art and science of growing plants,…

The science, art, and practice of managing and using the natural resources that occur on and in association with forested lands. Forestry is the management of forested lands (see illustration). It involves the planning and implementation of…

Plants that have altered genetic material (DNA) through recombinant DNA (rDNA) manipulation. Genetic engineering of plants allows for very specific genetic changes to be made to a plant's deoxyribonucleic acid (DNA), as opposed to the random…

Commercially grown plants that have altered genetic material through artificial recombinant manipulation. Genetic modification is the latest scientific tool for developing improved crop varieties. Such genetically modified (GM) crops can help to…

An organism that has had its genetic material manipulated or altered in a laboratory setting through the use of genetic or genomic engineering techniques. Genetically modified organisms (GMOs) are microorganisms, plants, or animals that have been…

Soil ingestion by animals. Grazing animals such as sheep and cattle ingest varying amounts of soil when they graze herbage contaminated with it.Pastures become contaminated with soil when livestock walk across the herbage, particularly in wet…

A tentative supposition with regard to an unknown state of affairs, the truth of which is thereupon subject to investigation by any available method, either by logical deduction of consequences which may be checked against what is known, or by…

The artificial application of water to the soil to produce plant growth. Irrigation also cools the soil and atmosphere, making the environment favorable for plant growth. The use of some form of irrigation (Fig. 1) is well documented throughout the…

A rare mineral tectosilicate found in volcanic rocks high in potassium and low in silica. Kaliophilite is one of three polymorphic forms of KAlSiO4; the others are the rare mineral kalsilite and an orthorhombic phase formed artificially at about…

Citrus limon, a small evergreen tree belonging to the order Sapindales that is cultivated for its fruit. In commercial terms, the lemon (Citrus limon; order Sapindales) is the most important of the acid citrus fruits (see illustration). It probably…

Lama glama, a member of the camel family (Camelidae) found only in South America. The llama (see illustration) is an artiodactyl, or even-toed ungulate, belonging to the mammalian family Camelidae. It has two toes on each foot. The llama is a…

The body of knowledge that concerns the fundamental nature, function, development, and use of formal models in science and technology. In its most general sense, a model is a proxy. A model is one entity used to represent some other entity for some…

Trees that can convert (fix) atmospheric nitrogen into a form that can be utilized for growth. The ability to convert (fix) atmospheric nitrogen into a form that can be used for plant growth is confined to bacteria and cyanobacteria. Plants fix…

A delicately flavored spice obtained from the nutmeg tree (Myristica fragrans), a native of the Moluccas (Maluku Islands or Spice Islands). The nutmeg tree is a dark-leafed evergreen that can reach 9–18 m (30–60 ft) in height and is a member of the…

A genus (Quercus) of trees, some of which are shrubby, with about 200 species, mainly in the Northern Hemisphere. About 50 species of oaks are native in the United States. All oaks have scaly winter buds, usually clustered at the ends of the twigs,…

An agricultural crop of the genus Avena grown for its grain and straw in most countries of the temperate zones of the world. Oats (Fig. 1) belong to the order Poales (Cyperales), family Poaceae (Gramineae), and genus Avena. The most important crop…

A warm-season annual, Hibiscus esculentus (also Abelmoschus esculentus), of Ethiopian origin. Okra, also called gumbo, is grown for its immature pods (see illustration), which are used generally in the preparation of soups, but are also eaten as a…

Any plant of the genus Olea in the order Lamiales (alternatively Scrophulariales), especially O. europaea, which is cultivated for its drupaceous fruit. Olea europaea is a small to medium-sized evergreen tree (Fig. 1). Olive fruits, both ripe…

A cool-season biennial, Allium cepa, that is cultivated for its edible bulb. The onion is of Asiatic origin and belongs to the plant order Asparagales; it was formerly included in the order Liliales. Related species are leek (A. porrum), garlic (A.…

Any of various evergreen trees of the genus Citrus, cultivated for its edible fruit. Orange trees (genus Citrus) belong to the family Rutaceae of the order Sapindales. The various trees classified as orange trees are most notable for producing…

An herb, also known as wild marjoram. The dried leaves of several species of aromatic plants are known as oregano; thus, oregano is a common name for a general flavor and aroma rather than the name of a specific plant. MarjoramEuropean oregano…

The genus Maclura of the mulberry family, with one species, M. pomifera. The osage orange tree may attain a height of 60 ft (18 m) and has yellowish bark, milky sap, simple entire leaves, strong axillary thorns, and aggregate green fruit that are…

Carica papaya, a semiwoody, usually single-stemmed, herbaceous plant cultivated for its fruit in tropical and subtropical regions. The papaya plant (Fig. 1) originated along the Caribbean lowlands of Mesoamerica and is now extensively and…

A type of pepper, Capsicum annuum, with nonpungent flesh, grown for its long red fruit. The paprika pepper (see illustration) is a member of the plant order Solanales (formerly assigned to Polemoniales) and is of American origin. It is most popular…

An annual leafy leguminous vine, Pisum sativum (order Fabales), cultivated for its smooth or wrinkled, round edible seeds, which are borne in dehiscent pods. The garden pea (Fig. 1) is one of the world's oldest cultivated crops. It is a native of…

A deciduous fruit tree species, Prunus persica, of the order Rosales. The peach (see illustration), taxonomically known as Prunus persica (order Rosales), is a notable fruit tree species that originated and was first cultivated in western China. It…

A long-season cultivar (cultivated variety) of muskmelon, Cucumis melo, of the gourd family. Persian melons (see illustration) are members of the family Cucurbitaceae (which includes melons, squashes, pumpkins, and cucumbers) in the order…

A deciduous fruit tree species, Diospyros kaki, in the ebony family (Ebenaceae). Persimmon trees (Fig. 1) originated in the subtropical regions of China, but were cultivated more extensively in Japan. At the present time, China, South Korea, and…

A type of pepper, Capsicum annuum, grown for its thick, sweet-fleshed red fruit. The pimento (see illustration) is a member of the plant order Solanales (formerly assigned to Polemoniales) and is of American origin. The pimento gets its name from…

A fiber, also known as pineapple fiber, obtained from the large leaves of the pineapple plant grown in tropical countries. Piña (also spelled pina) is a natural fiber (see illustration) that is white and especially soft and lustrous. In the…

Any tree of the genus Pinus, of the family Pinaceae, characterized by evergreen leaves, usually in tight clusters (fascicles) of two to five, rarely single. There are about 80 known species of pine distributed throughout the Northern Hemisphere.…

The edible seed of more than a dozen species of evergreen cone-bearing trees in the genus Pinus, native to the temperate zone of the Northern Hemisphere. The important pine nut–producing species are the stone pine (P. pinea) of southern Europe; the…

A low-growing perennial plant (genus Ananas) and its edible fruit, indigenous to the Americas. The cultivated varieties (cultivars) of pineapple belong to the species Ananas comosus (alternatively Ananas sativus) of the plant order Bromeliales or…

A small, spreading dioecious evergreen tree, Pistacia vera, of the Anacardiaceae family (order Sapindales), with leaves that have three to five broad leaflets and with large drupaceous fruit containing an edible seed (nut). The pistachio tree is…

Any of various smooth-skinned stone fruits grown on shrubs or small trees (genus Prunus, order Rosales). Plums are widely distributed in all land areas of the North Temperate Zone, where many species and varieties are adapted to different climatic…

A small deciduous tree, Punica granatum, belonging to the plant order Myrtales and cultivated for its reddish, pomelike fruit. The pomegranate is grown as an ornamental plant as well as for its fruit. Propagation is by cuttings and occasionally by…

Any tree of the genus Populus, family Salicaceae, marked by simple, alternate leaves that are usually broader than those of the willow, the other American representative of this family. Poplars have scaly buds, bitter bark, flowers and fruit in…

A plant belonging to the genus Solanum in the nightshade family (Solanaceae) that produces an edible tuber. There are more than 2000 species of Solanum (order Solanales), of which approximately 150 bear tubers. The potato of commerce, S. tuberosum…

Ipomoea batatas (order Solanales), a tropical vine having variously shaped leaves, purplish flowers, and a sweet, fleshy, edible tuberous root. The sweet potato (Fig. 1), occasionally spelled as one word (sweetpotato), was mentioned as being grown…