American Heritage® Dictionary of the English Language, Fourth Edition
- n. The process by which rocks are altered in composition, texture, or internal structure by extreme heat, pressure, and the introduction of new chemical substances.
Century Dictionary and Cyclopedia
- n. The process of metamorphosing, or changing the form or structure; specifically, chemical change and rearrangement of the constituents of a rock by which they are made to assume new forms and enter into new combinations, the most important result of these changes being that the rock becomes harder and more crystalline in structure. Thus, the metamorphic slates are crystalline schists. The sedimentary rocks, especially those made up of the debris of feldspathic minerals, are those most liable to undergo metamorphism; hence it is that the argillaceous rocks offer the most conspicuous examples of this process, and it is these which are most altered in external characters by it, foliation and slaty cleavage being often highly developed in the process. Volcanic rocks also are subject to metamorphic changes, although the results are usually much less conspicuous to the eye unaided by a microscope than in the case of the sedimentary deposits. Examples of metamorphism are the conversion of ordinary earthy limestone into crystalline marble, of argillaceous shales into various kinds of schists (mica-schist, talc-schist, etc.), and of sandstone into quartzite. Closely connected with the phenomena of metamorphism is the development in a rock of a slaty cleavage or of a foliated structure. Metamorphic agencies and the results which they have brought about have been much studied of late years by geologists, and the modern methods of lithological research have been most important aids in this direction. The most obvious and generally accepted classification of metamorphic action is into “contact” and “regional” metamorphism. In the case of contact metamorphism the changes observed are apparently due—in large part, at least—to the presence of an adjacent mass of rock, usually of an intrusive character, as when the strata are seen to have been altered along the walls of a dike. In the case of regional metamorphism, when large masses of rock are found to have been affected and rendered crystalline without any special cause being visible in the form of adjacent intrusive or igneous material, the phenomena are more difficult of explanation thau in the case of contact metamorphism. In the course of the numerous discussions of this subject a great number of newterms have been introduced, the meaning of which is, owing to the complexity of the phenomena and the imperfection of the observations, often rather obscure; some of these terms may here be cited. As synonyms of “regional” metamorphism, the epithets “normal” and “general” have been used by some authors, while others have indicated a desire to specialize in their application. Thus, Prestwich limits “normal metamorphism” to the changes due to central heat, and “regional metamorphism” to changes effected by the heat produced locally within the crust of the earth by transformation into heat of the mechanical work of compression or of crushing of parts of the earth. Bonney desires to reserve the phrase “regional metamorphism” for those ancient rocks occupying extensive areas of the earth's surface “which, whatever be their history, are in all probability by no means in their original condition.” Dana prefers “local” to “contact,” but does not use the two exactly as synonyms, since he makes local “include changes due to heated emanations and other conditions where there are no contacts”—in other words, he uses “local” rather as the opposite of “general,” ignoring the idea embodied in the term “contact,” namely that a visible cause of the observed metamorphism is present in the form of an adjacent mass of intrusive or heterogeneous rock. Kinahan proposes “metapepsis” and “paroptesis” as the synonyms of regional and contact metamorphism. “Why we need go to the Greek for [the] two words is not clear.” (Dana.) Many geologists are of the opinion that the movements which the rocks composing the earth's crust have undergone in certain regions, which movements must necessarily have been accompanied by pressure, stress, shearing, or “flow,” have been among the most important causes of metamorphic change. The most comprehensive term by which metamorphism originating in conditions of this kind has been designated is that introduced by Rosenbusch, “dynamical.” Other writers on this subject have used as being nearly or quite synonymous with “dynamical” the following: “pressure,” “compression,” “mechanical,” “friction,” “dislocation.” Judd has introduced the term “statical metamorphism” as indicating changes which may have taken place in deep-seated rocks quite independently of any movement to which they have been subjected. As designating and discriminating between various kinds of metamorphic changes, with special reference to the character of the results produced, Dana has introduced the terms “crystallinic,” “paramorphic,” and “metachemic.” The first of these implies a simple development of a crystalline condition in the original material, such, for instance, as takes place in the conversion of limestone into marble (“marmarosis” of Geikie); the second, a change from one paramorphic state to another, as from augite to hornblende; the third, a change through chemical transformations, as of chrysolite to serpentine. “Metasomatic metamorphism” (or, in one word, “metasomatosis”) and “methylosis” are terms which have been suggested in this connection. but which have met with little favor; they were apparently intended by their authors to include chemical changes similar to those which take place in the formation of pseudomorphs, and are allied to the “metachemic” of Dana. “Metastasis” and “metacrasis” are terms which have been coined, but have not become current—the one to denote changes somewhat similar to those included by Dana under “crystallinic,” the other (as defined by that author) to “denote changes like the conversion of a mass of mud into a mass of quartz with mica and other silicates.”
- n. geology The process by which rocks are changed into other forms by the application of heat and/or pressure.
- n. zoology The process by which insects development through life stages -- as, for example, those of embryo, larva, pupa and imago. The life cycle of the butterfly is one of complete metamorphosis, in which the embryo grows within the egg, hatches into the larval stage caterpillar, enters the pupal stage within its chrysalis, and finally emerges as an adult butterfly imago.
GNU Webster's 1913
- n. (Geol.) The state or quality of being metamorphic; the process by which the material of rock masses has been more or less recrystallized by heat, pressure, etc., as in the change of sedimentary limestone to marble.
- n. change in the structure of rock by natural agencies such as pressure or heat or introduction of new chemical substances
- From metamorphosis + -ism, after French métamorphisme. (Wiktionary)
- metamorph(ic) + -ism. (American Heritage® Dictionary of the English Language, Fourth Edition)
“Some geologists confine the term metamorphism to the changes involved in contact and dynamic metamorphism, and call the resulting products _metamorphic rocks_.”
“Basically, a process called metamorphism caused the basalts in Shenandoah to recrystallize with new minerals, such as chlorite, epidote, and albite, which help give the rocks their greenish hue.”
“Rocks are not permanent in their condition, but at practically all times and places are undergoing some kind of metamorphism which tends to adapt them to their environment.”
““Submicron magnetite grains and carbon compounds in Martian meteorite ALH84001: Inorganic, abiotic formation by shock and thermal metamorphism.””
“These mantle rocks also show a type of metamorphism found only in conditions of very high energy release.”
“It is an oil from Neem seeds, it is used as and anti fungal in gardening. .it also smells bad and drives off insects, those that do eat of it have their larval hormones messed up enough they cannot metamorphism to moths, it is also bitter, it has been used as a contraceptive in its native India.”
“Some metasiltstone or metasandstone occurs, but it is material of very low-grade metamorphism.”
“A key component was the discovery that processes currently observable - sedimentation, metamorphism and volcanic activity - working over long periods of time, not only could account for the sorts of rocks we actually find, but could account for them better than earlier catastrophic scenarios in most instances.”
“Geologically this assemblage of unusual forms of contact metamorphism with simultaneously intruded acidic and basic magmas is unique in the British Tertiary Volcanic province.”
“Geology and metamorphism of the Nanda Devi region, Kumaon, Higher Himalaya, India.”
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