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METEORITE
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METEORITE , a See also:mass of See also:mineral See also:matter which has reached the See also:earth's See also:surface from See also:outer space. Observation teaches that the fall of a meteorite is often preceded by the See also:flight of a fireball (see See also:METEOR) through the See also:sky, and by one or more loud detonations. It was inferred by Chladni (1794) that the See also:fire-See also:ball and the detonations result from the See also:quick passage of the meteorite through the earth's See also:atmosphere.
The fall of stones from the sky, though not credited by scientific men till the end of the 18th See also:century, had been again and again placed on See also:record. One of the most famous of meteorites See also:fell in See also:Phrygia and was worshipped there for many generations under the name of See also:Cybele, the See also:mother of the gods. After an See also:oracle had declared that See also:possession of the See also: It was not till scientific men gave See also:credence to the reports of the fall of heavy bodies from the sky that steps were taken for the formation of meteorite collections. The See also:British Museum (Natural History) at See also:South See also:Kensington now contains specimens belonging to 566 distinct falls; of these falls 325 have been actually observed; the remaining specimens are inferred to have come from outer space, because their characters are similar to those of the masses which have been seen to fall. Of these meteorites the following twelve have fallen within the British Isles: See also:Place. Date. In See also:England. Wold Cottage, Thwing, See also:York- Dec. 13, 1795. See also:shire . . Launton, See also:Oxfordshire Feb. 15, 183o. Aldsworth, See also:Gloucestershire Aug. 4, 1835. See also:Rowton, See also:Shropshire . See also:April 20, 1876.
See also:Middlesbrough, See also:Yorkshire See also: April 29, 1844. Dundrum, Tipperary Aug. 12, 1865. Crumlin, See also:Antrim . Sept. 13, 1902. Meteoritic falls are See also:independent of thunderstorms and all other terrestrial circumstances; they occur at all See also:hours of the day and See also:night, and at all seasons of the year; they favour no particular latitudes. The number of stones which reach the ground from one fireball is very variable. In each of the two Yorkshire falls only one stone was found; the See also:Guernsey See also:County meteor yielded 30; at See also:Toulouse, as many as 350 are estimated to have fallen; at Hessle, over 500; at Knyahinya, more than 1000; at L'Aigle, from r000 to 2000; at both See also:Pultusk and Mocs no fewer than roo,000 are estimated to have reached the earth's surface. The largest single mass seen to fall is one of those which came down at Knyahinya, See also:Hungary, in 1866, and weighed 5471b; but far larger masses, inferred from their characters to be meteorites, have been met with. The larger of the Cranbourne masses, now in the British Museum (Natural History), before rusting weighed 32 tons; the largest of the masses brought by Lieut. See also:Peary from western See also:Greenland weighs 362 tons. A mass found at Bacubirito in See also:Mexico is 13 ft. long, 6 ft. wide and 5 ft. thick, and is estimated to weigh 50 tons. From observations of the path and time of flight of the luminous meteor it is calculated that meteorites enter the earth's atmosphere with See also:absolute velocities ranging from ro to 45 M. a second; but the See also:speed of a meteorite after the whole of the resisting atmosphere has been traversed is extremely small and comparable with that of an See also:ordinary falling See also:body. According to See also:Professor A. S. See also:Herschel's experiments, the meteorite which fell at Middlesbrough must have struck the ground with a velocity of only 412 ft. a second. In the See also:case of the Hessle fall, several stones fell on the See also:ice, which was only a few inches thick, and rebounded without breaking the ice or being broken themselves. The depth to which a meteorite penetrates depends on the speed, See also:form, See also:weight and See also:density of the meteorite and on the nature of the ground. At Stannern a meteoric stone weighing 2 lb entered to a depth of only 4 in.; the large Knyahinya stone already mentioned made a hole r 1 ft. deep. The See also:area of the earth's surface occupied by towns and villages being comparatively small, the See also:probability of a shower of stones falling within a town is extremely See also:minute; the likelihood of a living creature being struck is still more remote. The first Yorkshire stone, that of Wold Cottage, struck the ground only 10 yds. from a labourer; the second, that of Middlesbrough, fell on the railroad only 40 yds. away from some platelayers at See also:work; a stone completely buried itself in the See also:highway at Kaba; one fell between two carters on the road at Charsonville, throwing the ground up to a height of 6 ft.; the Tourinnes-la-See also:Grosse meteorite See also:broke the See also:pavement and was broken itself; the Krahenberg stone fell within a few paces of a little girl; the See also:Angers stone fell See also:close to a See also:lady See also:standing in her See also:garden; the See also:Braunau mass went through the roof of a cottage; at See also:Macao, in See also:Brazil, where there was a shower of stones, some oxen are said to have been killed; at Nedagolla, in See also:India, a See also:man was so near that he was stunned by the See also:shock; while at See also:Mhow, also in India, a man was killed in 1827 by a stone which is a true meteorite, and is represented by fragments in museum collections. Though the surface of a meteoric stone becomes very hot during the See also:early See also:part of the flight through the See also:air, it is cooled again during the later and slower part of the flight. Meteorites are generally found to be warm to the See also:touch if immediately dug out; at the moment of their impact they are not hot enough to See also:char woody fibre on which they See also:chance to fall, nor is the surface then soft, for terrestrial matter with which the surface comes into contact makes no impression upon the meteorite. Where many stones fall at the same time they are generally distributed over a large area elongated in the direction of the flight of the luminous meteor, and the largest stones generally travel farthest. At Hessle, for instance, the stones were distributed over an area of to m. long and 3 M. broad. Meteorites are almost invariably found to be completely covered with a thin crust such as would be caused by intense See also:heating of the material for a See also:short time; its thinness shows the slight depth to which the See also:heat has had time to penetrate. They are presumably See also:cold and invisible when they enter the earth's atmosphere, and become heated and visible during their passage through the air; doubtless the greater -part of the superficial material flicks off as the result of the sudden heating and is See also:left behind floating in the air as the trail of the meteor. The crust varies in aspect with the mineral See also:composition of the meteorite; it is generally black; it is in most cases dull but is sometimes lustrous; more rarely it is dark-See also:grey in See also:colour. Each stone of a shower is in See also:general completely covered with crust; but occasion-ally, as in the case of the Butsura fall, stones found some See also:miles apart See also:fit each other closely and the fitting surfaces are encrusted, showing that a meteorite may break up during a See also:late and cool See also:stage of the flight through the atmosphere. A meteorite is generally covered with pittings which have been compared in See also:size and form to thumbmarks; the pittings are probably caused by the unequal conductivity, fusibility and frangibility of the superficial material. As picked up, See also:complete and covered with crust, meteorites are always irregularly-shaped fragments, such as would be obtained on breaking up a See also:rock presenting no regularity of structure. About one-third, and those the most See also:common, of the chemical elements at See also:present recognized as constituents of the earth's crust have been met with in meteorites; no new chemical See also:element has been discovered. The most frequent or plentiful in their occurrence are: See also:aluminium, See also:calcium, See also:carbon, See also:iron, See also:magnesium, See also:nickel, See also:oxygen, See also:phosphorus, See also:silicon and See also:sulphur; while less frequently or in smaller quantities are found See also:antimony, See also:arsenic, See also:chlorine, See also:chromium, See also:cobalt, See also:copper, See also:hydrogen, See also:lithium, See also:manganese, See also:nitrogen, See also:potassium, See also:sodium, See also:strontium, See also:tin, See also:titanium, See also:vanadium. The existence of minute traces of several other elements has been announced; of these See also:special mention may be made of See also:gallium, See also:gold, See also:iridium, See also:lead, See also:platinum and See also:silver. Iron occurs chiefly in See also:combination with nickel, and phosphorus almost always in combination with both nickel and iron (schreibersite); carbon occurs both as indistinctly crystallized See also:diamond and as graphitic carbon, the latter generally being amorphous, but occasionally having the forms of cubic crystals (cliftonite); See also:free phosphorus has been found in one meteorite; free sulphur has also been observed, but may have resulted from the decomposition of a sulphide since the fall of the stone. Of the mineral constituents of meteorites, the following are by many mineralogists regarded as still unrepresented among nativeterrestrial products: cliftonite, a cubic form of graphitic carbon; phosphorus; various See also:alloys of nickel and iron; moissanite, silicide of carbon; cohenite, See also:carbide of iron and nickel (corresponding to cementite, carbide of iron, found in artificial iron); schreibersite., phosphide of iron and nickel; troilite, protosulphide of iron; oldhamite, sulphide of calcium: osbornite, oxysulphide of calcium and titanium or See also:zirconium; daubreelite, sulphide of iron and chromium; lawrencite, protochloride of iron; asmanite, a See also:species of See also:silica; maskelynite, a singly refractive mineral with the chemical composition of See also:labradorite; weinbergerite, a silicate intermediate in chemical composition to See also:pyroxene and See also:nepheline. Of these troilite is perhaps identical with some varieties of terrestrial See also:pyrrhotite; asmanite has characters which approach very closely to those of terrestrial See also:tridymite; maskelynite, according to one view, is the result of See also:fusion of labradorite, according to another view, is an independent species chemically related to See also:leucite. Other compounds are present corresponding to the following terrestrial minerals: See also:olivine and forsterite; See also:enstatite and See also:bronzite; See also:diopside and See also:augite; See also:anorthite, labradorite and See also:oligoclase; See also:magnetite and See also:chromite; See also:pyrites; pyrrhotite; breunnerite. See also:Quartz (silica), the most common of terrestrial minerals, is absent from the stony meteorites; but from the See also:Toluca meteoric iron microscopic crystals have been obtained of which some have certain resemblances to quartz, and others to See also:zircon. Free silica is present in the Breitenbach meteorite but as asmanite. In addition to the above there are several compounds or mixtures of which the nature has not yet been satisfactorily ascertained. Meteorites are conveniently distributed into three classes, which pass more or less gradually into each other: the first (siderites or meteoric irons) includes all those which consist mainly of metallic iron alloyed with nickel; only nine of them have been actually seen to fall; the second (siderolites) includes those in which metallic iron (alloyed with nickel) and stony matter are present in large proportion; few of them have been seen to fall; those of the third class (aerolites or meteoric stones) consist almost entirely of stony matter; nearly all have been seen to fall. In the meteoric irons the iron generally varies from 8o to 95 % and the nickel from 6 to 1o%; the latter is generally alloyed with the iron, and several alloys or mixtures have been distinguished by special names (kamacite, taenite, plessite). Troilite is frequently present as plates, See also:veins or large nodules, sometimes surrounded by See also:graphite; schreibersite is almost always present, and occasionally also daubreelite. The compositeness and the structure of meteoric iron are well shown by the figures generally called into existence when a polished surface is etched by means of acids or See also:bromine-See also:water; they are due to the inequality of the See also:etching See also:action on thick and thin plates of various constituents, the plates being composed chiefly of two nickel-iron materials (kamacite and taenite). A third nickel-iron material (plessite) fills up the spaces formed by the intersection of the See also:joint plates of kamacite and taenite; it is probably not an independent substance but an intimate intergrowth of kamacite and taenite. The figures were first observed in 18o8 and are generally termed "Widmanstatten figures " in See also:honour of their discoverer; the plates which give rise to them are parallel to the faces of the See also:regular See also:octahedron, and such masses have therefore an octahedral structure. A small number of the remaining masses have cubic cleavage; instead of Widmanstatten figures they yield See also:fine linear furrows when etched; the furrows were found by See also:Neumann in 1848 to have directions such as would result from twinning of the See also:cube about an octahedral See also:face; they are known as " Neumann lines." For meteoric irons of cubic structure the percentage of nickel is See also:lower than 6 or q; for those of octahedral structure it is higher than 6 or 7; the plates of kamacite are thinner, and the structure therefore finer the higher the percentage of that See also:metal. A considerable number of meteoric irons, however, show no crystalline structure at all, and have percentages of nickel both below and above 7; it has been suggested that each of these masses may once have had crystalline structure and that it has disappeared as a result of prolonged heating throughout the mass while the meteorite has been passing near a See also:star.
An investigation of the changes of the magnetic See also:permeability of the See also:Sacramento meteoric iron with changing temperature led Dr S. W. J. See also: Wulfing, Die Meteoriten in Sammlungen and ihre Literatur (Tiibingen, 1897). (L. F.) largely of plates of nickel-iron containing about 7% of nickel (kamacite), separated from each other . by thin plates of a nickel-iron constituent (taenite), containing about 27% of nickel and having different thermomagnetic characters from those of kamacite; he suggests, however, that taenite is not a definite chemical See also:compound but a eutectic mixture of kamacite and a nickel-iron compound containing not less than 37 % of nickel. About eleven out of every twelve of the known meteoric stones belong to a See also:division to which Rose gave the name " chondritic " (X6vapos, a See also:grain); they present a very fine-grained but crystalline See also:matrix or See also:paste, consisting of olivine and enstatite or bronzite, with more or less nickel-iron, troilite, chromite, augite and triclinic feldspar; through this paste are disseminated See also:round chondrules of various sizes and generally with the same mineral composition as the matrix; in some cases the chondrules consist wholly or in great part of See also:glass. Some meteorites consist almost solely of chondrules; others contain only few; in some cases the chondrules are easily separable from the surrounding material. In mineral composition chondritic meteorites approximate more or less to terrestrial lherzolites. A few meteorites belonging to the chondritic division are remarkable as containing carbon in combination with hydrogen and oxygen; those of See also:Alais and Cold Bokkeveld are See also:good examples. The remaining meteoric stones are without chondrules and contain little or no nickel-iron; of these the following may be mentioned as illustrative of the varieties of mineral composition: Juvinas, consisting essentially of anorthite and augite; See also:Petersburg, of anorthite, augite and olivine, with a little chromite and nickel-iron (both Juvinas and Petersburg may be compared to terrestrial See also:basalt); Sherghotty, chiefly of augite and maskelynite; See also:Angra dos Reis, almost wholly of augite, but olivine is present in small proportion; Bustee, of diopside, enstatite and a little triclinic feldspar, with some nickel-iron, oldhamite and osbornite; Bishopville, of enstatite and triclinic feldspar, with occasional augite, nickel-iron, troilite and chromite; Roda, of olivine and bronzite; and Chassigny, consisting of olivine with enclosed chromite, and thus mineralogically identical with terrestrial dunite. Almost all meteoric stones appear to be made up of irregular angular fragments, and some of them See also:bear a close resemblance to volcanic tuffs. In the large See also:group of chondritic stones, chondrules or spherules, some of which can only be seen under the See also:microscope while others reach the size of a See also:walnut, are embedded in a matrix apparently made up of minute splinters such as might result from the fracture of the chondrules them-selves. In fact, until recently it was thought by some mineralogists that the chondrules owe their form, not to See also:crystallization, but to See also:friction, and that the matrix was actually produced by the wearing down of the chondrules through frequent collision with. each other as oscillating components of a See also:comet or during repeated ejection from a volcanic vent of some small See also:celestial body. Chondrules have been observed, however, presenting forms and crystalline surfaces incompatible with such a mode of formation, and others have been described which exhibit features resulting from mutual interference during their growth. The chondritic structure is different from anything which has yet been observed in terrestrial rocks, and the chondrules are distinct in See also:character from those observed in See also:perlite and See also:obsidian. It is now generally believed that the structural features of meteoric stones are the result of hurried crystallization.
No organized matter has been found in meteorites and they have brought us, therefore, no See also:evidence of the existence of living beings outside our own See also:world.
Aurnoairlrs.—The literature consists chiefly of See also:memoirs dispersed through the See also:journals of scientific See also:societies. The following See also:separate See also:works may be consulted: A. Brezina, Die Meteoriten-Sammlung d. k-k. See also:min. Hofkabinetes in Wien (See also:Vienna, 1896); A. Brezina u. E. See also:Cohen, Die Structur and die Zusammensetzung der Meteoriten (Stuttgart, 1886-1887) ; P. S. See also:Bigot de Morogues, Memnire historique et physique sur See also:les chutes See also:des pierres (See also: Additional information and CommentsThere are no comments yet for this article.
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