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Agglomerates are large blocks of igneous rocks often found at the exit points of volcanoes. Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Sedimentary, volcanic, plutonic, metamorphic rock types of North America. ... This article is about volcanoes in geology. ...

Historical description of agglomerates

The following text is from the 1911 Encyclopedia Britannica

AGGLOMERATE (from the Lat. agglomerare, to form into a ball, glomus, glomeris), a term used in botany, meaning crowded in a close cluster or head, and, in geology, applied to the accumulations of coarse volcanic ejections such as frequently occur near extinct or active volcanoes. Agglomerates in the geological sense, with which this article is concerned, consist typically of blocks of various igneous rocks, mixed often with more or less material of rudimentary origin and embedded in a finer-grained matrix, similar in nature to the coarser fragments. As distinguished from ordinary ash beds or tuffs, they are essentially coarser, less frequently well-bedded; they are less persistent and tend to occur locally, but may attain a very great thickness. Showers of fine ash may be distributed over a wide area of country and will form thin layers of great extent. Coarser accumulations gather only near the actual foci of eruption (craters, fissures, etc.). When the activity of a volcanic vent comes to an end, the orifice is often choked by masses of debris, which will in time become compacted into firm agglomerates. Hence rocks of this type very commonly mark the sites of necks, the remains of once-active volcanic craters. In this connection they are of especial interest to geologists, as it is always important to be able to locate the exact points at which volcanic products, such as lavas and ash-beds, were emitted. Botany is the scientific study of plant life. ... See: In astrophysics and astrometry: star cluster, galaxy cluster In molecular physics and solid state physics: A collaboration of (mostly equal) atoms, halfway between molecules and crystals; see cluster (physics) In music: tone cluster In statistics: cluster sampling or cluster analysis metall cluster In economics: Porters cluster Techno cluster... Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history, and the processes that shape it. ... In biology and ecology, extinction is the ceasing of existence of a species or group of species. ... active active lifestyle active volcano active grammatical voice See also Activation Activity This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Wiktionary has a definition of: Matrix The word matrix (plural matrices, or less often, matrixes) has several meanings. ... Diamond Head, a well-known backdrop to Waikiki in Hawaii, is an ash cone that solidified into tuff Volcanic ash is the term for very fine rock and mineral particles less than 2 mm in diameter that are ejected from a volcanic vent. ... Tuff - Wikipedia /**/ @import /skins-1. ... The word focus (pl. ... The word crater may refer to A landform resembling a pit or depression in the topography that can be formed in several ways: speculation exists that a meteorite impact with another body can cause an impact crater, an electrical discharge on any scale tends to form circular craters, volcanic activity... Fissure (Latin fissura, Plural fissurae) is a groove, natural division, deep furrow, or cleft found in the brain, spinal cord, and liver; or an unnatural tract found most commonly in the anus. ... A vent can refer to: A volcano An outlet of a biological ventilation system that allows the exchange of air; see gas exchange The discharge from a combustion chamber; see chimney This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... In a typical mammalian body such as the human body, the body orifices are: the nostrils, for breathing and the associated sense of smell the mouth, for eating and vocalizations such as speech the ear canals, for the sense of hearing the anus, for defecation the urethra, for urination (and... Debris (French, pronounced (IPA) dibri) is a word used to describe the remains of something that has been otherwise destroyed. ... A geologist is a contributor to the science of geology. ... Lava is molten rock that a volcano expels during an eruption. ...

The blocks in agglomerates vary greatly in size. Some are thirty or forty feet in diameter, and weigh many tons; these are usually pieces of the strata through which the volcano has forced an outlet. They are never far from the crater; most of them, in fact, lie within its boundaries, and cases are known in which enormous masses of this kind (half an acre in area) have been found in such situations. They are masses which have been dislodged, by fissures and landslides, from the crater's walls and have tumbled into the cavity. Pieces of sandstone, limestone and shale occur in the agglomerates mixed with volcanic materials, and very often have been baked and partly recrystallized by contact with the hot igneous rocks and the gases discharged by the volcano. At Vesuvius such blocks of altered limestone are rich in new minerals and are well known to collectors. The word ton or tonne is derived from the Old English tunne, and ultimately from the Old French tonne, and referred originally to a large cask with a capacity of 252 wine gallons, which holds approximately 2100 pounds of water. ... For discussion regarding the term strata as used in geology, see stratum. ... An acre is a measure of land area in Imperial units or U.S. customary units. ... This entry refers to the geological term landslide. ... Red Sandstone in Wyoming Sandstone is an arenaceous sedimentary rock composed mainly of feldspar and quartz and varies in colour (in a similar way to sand), through grey, yellow, red, and white. ... Limey shale overlaid by limestone. ... Shale Shale is a fine-grained sedimentary rock whose original constituents were clays or muds. ... Mount Vesuvius (Italian: Monte Vesuvio) is a volcano east of Naples, Italy, located at 40°49′N 14°26′ E. It is the only active volcano on the European mainland, although it is not currently erupting. ...

Agglomerates also are usually full of volcanic bombs. These are spongy globular masses of lava which have been shot from the crater at a time when liquid molten lava was exposed in it, and was frequently shattered by the sudden outbursts of steam. These bombs were more or less viscous at the moment of ejection and by rotation in the air acquired their spheroidal form. They are commonly one or two feet in diameter, but specimens as large as nine or twelve feet have been observed. There is less variety in their composition at any volcanic centre than in the case of the foreign blocks above described. They correspond in nature to the lava which at the time fills the crater of the volcano, and as this varies only very slowly the bombs belong mostly to only a few kinds of rock and are similar in composition to the lava flows. Volcanic bombs are globules of melted rock (tephra) larger than 2. ... In physical chemistry and in engineering, steam refers to vaporized water. ... Viscosity is a measure of the resistance of a fluid to deformation under shear stress. ... A spheroid is a quadric surface in three dimensions obtained by rotating an ellipse about one of its principal axes. ... In biology, specimen is an individual animal or a plant or a microorganism that is used as a representative to study the properties of the whole population of that species. ...

Crystalline masses of a different kind occur in some numbers in certain agglomerates. They consist of volcanic minerals very much the same as those formed in the lavas, but exhibiting certain peculiarities which indicate that they have formed slowly under pressure at considerable depths. Hence they bear a resemblance to plutonic igneous rocks, but are more correctly to be regarded as agglomerations of crystals formed within the liquid lava as it slowly rose towards the surface, and at a subsequent period cast out by violent steam explosions. The sanidinites of the Eifel belong to this group. At Vesuvius, Ascension, St Vincent and many other volcanoes, they form a not inconsiderable part of the coarser ash-beds. Their commonest minerals are olivine, anorthite, hornblende, augite, biotite and leucite. Crystal (disambiguation) Insulin crystals A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... In geology an intrusion is usually a body of igneous rock that has crystallized from a molten magma below the surface of the Earth. ... Quartz crystal A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... Violence is a general term to describe actions, usually deliberate, that cause or intend to cause injury to people, animals, or non-living objects. ... The Eifel is a hilly region in Germany. ... The Ascension is one of the great feasts in the Christian liturgical calendar, and commemorates the bodily Ascension of Jesus into Heaven forty days after his resurrection from the dead. ... Saint Vincent may refer to: Saint Vincent (island) Saint Vincent and the Grenadines São Vicente Saint Vincent de Paul Saint Vincent Ferrer Saint Vincent of Lerins Saint Vincent of Saragossa Saint Vincent Pallotti Saint-Vincent, a municipality of the Valle dAosta, in Italy St. ... Olivine The mineral olivine is a magnesium iron silicate with the formula (Mg,Fe)2SiO4 in which the ratio of magnesium and iron varies between the two endmembers of the series: forsterite (Mg-rich) and fayalite (Fe-rich). ... Anorthite is one of the plagioclase feldspars, an important group of minerals abundant in the Earths crust. ... Amphibole (Hornblende) The mineral hornblende is a complex silicate which is an isomorphous mixture of three molecules; a calcium-iron-magnesium silicate, an aluminium-iron-magnesium silicate, and an iron-magnesium silicate. ... Augite Categories: Mineral stubs | Minerals | Silicate minerals ... A Biotite slice Biotite is a common silicate mineral that contains potassium, magnesium, iron and aluminium. ... Leucite or amphigene is a rock-forming mineral composed of potassium and aluminium metasilicate KAl(SiO3)2. ...

Agglomerates occur wherever volcanoes are known. In many parts of Britain they attain a great development either in beds alternating with lavas or as the material occupying necks. In the latter case they are often penetrated by dikes. They also show a steep, angular, funnel-shaped dip (e.g. Arthur's Seat, Edinburgh), and may contain thin layers of clay or ashy sand-stone, which gathered in the crater during intervals of repose. Dyke (normal International spelling) or Dike (normal American spelling) can mean several things: A dyke / dike is a long wall built to keep out the sea or enclose land. ... Arthurs Seat most frequently refers to Arthurs Seat, Edinburgh, Scotland Other references to Arthurs Seat: Places named for King Arthur; most frequently to be found in England. ... Edinburghs location in Scotland Edinburgh viewed from Arthurs Seat. ... Clay is a generic term for an aggregate of hydrous silicate particles less than 4 μm (micrometres) in diameter. ...