Ilmenite is the titanium-iron oxide mineral with the idealized formula FeTiO3. It is a weakly magnetic black or steel-gray solid, from the commercial perspective, ilmenite is the most important ore of titanium. Ilmenite is the source of titanium dioxide, which is used in paints, plastics, sunscreen, food. Ilmenite crystallizes in the trigonal system, containing high spin ferrous centers, ilmenite is paramagnetic. Ilmenite is commonly recognized in altered igneous rocks by the presence of an alteration product. Often ilmenites are rimmed with leucoxene, which allows ilmenite to be distinguished from magnetite, the example shown in the image at right is typical of leucoxene-rimmed ilmenite. In reflected light it may be distinguished from magnetite by more pronounced reflection pleochroism, samples of ilmenite exhibit a weak response to a hand magnet. Ilmenite most often contains appreciable quantities of magnesium and manganese and the chemical formula can be expressed as O3. Ilmenite forms a solution with geikielite and pyrophanite which are magnesian.
At higher temperatures it has been demonstrated there is a solid solution between ilmenite and hematite. There is a miscibility gap at lower temperatures, resulting in a coexistence of two minerals in rocks but no solid solution. This coexistence may result in exsolution lamellae in cooled ilmenites with more iron in the system than can be accommodated in the crystal lattice. Altered ilmenite forms the mineral leucoxene, an important source of titanium in heavy mineral sands ore deposits, leucoxene is a typical component of altered gabbro and diorite and is generally indicative of ilmenite in the unaltered rock. Ilmenite is an accessory mineral found in metamorphic and igneous rocks. It is found in large concentrations in layered intrusions where it forms as part of a layer within the silicate stratigraphy of the intrusion. Ilmenite generally occurs within the portion of such intrusions. Magnesian ilmenite is indicative of kimberlitic paragenesis and forms part of the MARID association of minerals assemblage of glimmerite xenoliths, manganiferous ilmenite is found in granitic rocks and in carbonatite intrusions where it may contain anomalous niobium.
Many mafic igneous rocks contain grains of magnetite and ilmenite
Chalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical formula CuFeS2 and it has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green tinged black, on exposure to air, chalcopyrite oxidises to a variety of oxides and sulfates. Associated copper minerals include the sulfides bornite, covellite, carbonates such as malachite and azurite, chalcopyrite is rarely found in association with native copper. Natural chalcopyrite has no solid solution series with any other sulfide minerals, there is limited substitution of Zn with Cu despite chalcopyrite having the same crystal structure as sphalerite. Minor amounts of such as Ag, Au, Cd, Co, Ni, Pb, Sn. Selenium, Bi, Te, and As may substitute for sulfur in minor amounts, chalcopyrite is present with many ore-bearing environments via a variety of ore forming processes. Chalcopyrite is present in volcanogenic massive sulfide ore deposits and sedimentary exhalative deposits, chalcopyrite is concentrated in this environment via fluid transport.
Porphyry copper ore deposits are formed by concentration of copper within a granite stock during the ascent, chalcopyrite in this environment is produced by concentration within a magmatic system. Chalcopyrite is a mineral in Kambalda type komatiitic nickel ore deposits. In this environment chalcopyrite is formed by a sulfide liquid stripping copper from an immiscible silicate liquid, chalcopyrite is the most important copper ore. The largest deposit of nearly pure chalcopyrite ever discovered in Canada was at the end of the Temagami Greenstone Belt where Copperfields Mine extracted the high-grade copper. Chalcopyrite is present in the supergiant Olympic Dam Cu-Au-U deposit in South Australia, chalcopyrite may be found in coal seams associated with pyrite nodules, and as disseminations in carbonate sedimentary rocks. Crystallographically the structure of chalcopyrite is closely related to that of zinc blende ZnS, the unit cell is twice as large, reflecting an alternation of Cu+ and Fe3+ ions replacing Zn2+ ions in adjacent cells.
In contrast to the pyrite structure chalcopyrite has single S2− sulfide anions rather than disulfide pairs, another difference is that the iron cation is not diamagnetic low spin Fe as in pyrite. Classification of minerals List of minerals Kesterite
Magnetite is a mineral and one of the main iron ores. With the chemical formula Fe3O4, it is one of the oxides of iron, Magnetite is ferrimagnetic, it is attracted to a magnet and can be magnetized to become a permanent magnet itself. It is the most magnetic of all the minerals on Earth. Naturally-magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, today it is mined as iron ore. Small grains of magnetite occur in almost all igneous and metamorphic rocks, Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and leaves a black streak. The chemical IUPAC name is iron oxide and the chemical name is ferrous-ferric oxide. In addition to rocks, magnetite occurs in sedimentary rocks, including banded iron formations and in lake. Magnetite nanoparticles are thought to form in soils, where they probably oxidize rapidly to maghemite, Magnetite has an inverse spinel crystal structure. As a member of the group, it can form solid solutions with similarly structured minerals, including ulvospinel.
Titanomagnetite, known as titaniferous magnetite, is a solution between magnetite and ulvospinel that crystallizes in many mafic igneous rocks. Titanomagnetite may undergo oxyexsolution during cooling, resulting in ingrowths of magnetite and ilmenite, Magnetite has been important in understanding the conditions under which rocks form. Magnetite reacts with oxygen to produce hematite, and the pair forms a buffer that can control oxygen fugacity. Commonly, igneous rocks contain solid solutions of both titanomagnetite and hemoilmenite or titanohematite, Magnetite is produced from peridotites and dunites by serpentinization. Lodestones were used as a form of magnetic compass. At low temperatures, magnetite undergoes a crystal structure phase transition from a structure to a cubic structure known as the Verwey transition. The Verwey transition occurs around 121 K and is dependent on size, domain state. An isotropic point occurs near the Verwey transition around 130 K, the Curie temperature of magnetite is 858 K.
Magnetite is sometimes found in large quantities in beach sand. Such black sands are found in places, such as Lung Kwu Tan of Hong Kong, California of the United States
Gabbro refers to a large group of dark, often phaneritic, mafic intrusive igneous rocks chemically equivalent to basalt. It forms when magma is trapped beneath the Earths surface. Much of the Earths oceanic crust is made of gabbro, formed at mid-ocean ridges, Gabbro is found as plutons associated with continental volcanism. Due to its variant nature, the term gabbro may be applied loosely to a range of intrusive rocks. The term gabbro was used in the 1760s to name a set of types that were found in the ophiolites of the Apennine Mountains in Italy. Then, in 1809, the German geologist Christian Leopold von Buch used the term more restrictively in his description of these Italian ophiolitic rocks and he assigned the name gabbro to rocks that geologists nowadays would more strictly call metagabbro. Von Buch named gabbro after Gabbro, a village in Rosignano Marittimo municipality of Tuscany, Gabbro is dense, greenish or dark-colored and contains pyroxene and minor amounts of amphibole and olivine.
The pyroxene content is mostly clinopyroxene, generally augite, but small amounts of orthopyroxene may be present, if the amount of orthopyroxene is more than 95% of the total pyroxene content, the rock is termed norite. On the other hand, gabbro has more than 95% of its pyroxenes in the form of the monoclinic clinopyroxene/s, the calcium rich plagioclase feldspar and pyroxene content vary between 10% - 90% in gabbro. If more than 90% plagioclase is present, the rock is an anorthosite, if on the other hand, the rock contains more than 90% pyroxenes, it is termed pyroxenite. Gabbro may contain amounts of olivine and biotite. The quartz content in gabbro is less than 5% of total volume, quartz gabbros or monzogabbros are known to occur, for example the cizlakite at Pohorje in northeastern Slovenia, and are probably derived from magma that was over-saturated with silica. Gabbros contain minor amounts, typically a few percent, of iron-titanium oxides such as magnetite, Gabbro is generally coarse grained, with crystals in the size range of 1 mm or greater.
Finer grained equivalents of gabbro are called diabase, although the term microgabbro is often used when extra descriptiveness is desired, Gabbro may be extremely coarse grained to pegmatitic, and some pyroxene-plagioclase cumulates are essentially coarse grained gabbro, some may exhibit acicular crystal habits. Gabbro is usually equigranular in texture, although it may be porphyritic at times, cumulate gabbros are more properly termed pyroxene-plagioclase adcumulate. Gabbro is an part of the oceanic crust, and can be found in many ophiolite complexes as parts of zones III. Long belts of gabbroic intrusions are typically formed at proto-rift zones and around ancient rift zone margins, mantle plume hypotheses may rely on identifying mafic and ultramafic intrusions and coeval basalt volcanism. It is better to base a rock definition on descriptive characteristics of the rather than how or where it was formed
Keetmanshoop is a city in the ǁKaras Region of southern Namibia, lying on the Trans-Namib Railway from Windhoek to Upington in South Africa. It is named after Johann Keetman, a German industrialist and benefactor of the city, the town is situated in a semi-arid area, normally receiving an annual average rainfall of only 152 millimetres, although in the 2010/2011 rainy season 254 millimetres were measured. Before the colonial era, the settlement was known as ǂNuǂgoaes or Swartmodder, the first white settler, Guilliam Visagie, arrived here in 1785. When in February 1850 the Kharoǃoan clan split from the Red Nation, in 1860 the Rhenish Missionary Society founded a mission there to christianise the local Nama. The first missionary, Johann Georg Schröder, arrived in Keetmanshoop on April 14,1866, the mission station was named after the German trader and director of the Rhenish Missionary Society Johann Keetman who supported the mission financially. He never actually visited the place himself, Keetmanshoop has a hot desert climate, with long, very hot summers and warm winters.
The annual mean temperature is 21.1 °C with an annual high of 28.8 °C. The climate is characterized by sunshine and dryness as well as moderate heat all year long, the Rhenish Missionary Church was erected in 1895, it now contains a museum. It was declared a monument in 1978 and is a well-known landmark. Its unique combination of Gothic architecture cast in African stone makes it one of the masterpieces in the country. Other notable buildings are the Schützenhaus, the station building. The town is situated near two quiver tree forests, one of them being a monument and a major tourist attraction of Namibia. Also close to Keetmanshoop is the Naute Dam, J. Stephanus Stadium is located in Keetmanshoop and is home to Fedics United F. C. a football team in the Namibia Premier League. Keetmanshoop is an important center of the Karakul sheep farming community, Keetmanshoop is governed by a municipality council that currently has seven seats. In the 2010 local authority election, a total of 3,156 votes were cast in the city, SWAPO won with approximately 48% of the vote.
Of the three other parties seeking votes in the election, RDP received approximately 35% of the vote, followed by the Democratic Party and the Democratic Turnhalle Alliance
Biotite is a common phyllosilicate mineral within the mica group, with the approximate chemical formula K 3AlSi 3O102. Hausmann in 1847 in honor of the French physicist Jean-Baptiste Biot, magnesium, silicon and hydrogen form sheets that are weakly bound together by potassium ions. It is sometimes called iron mica because it is more iron-rich than phlogopite and it is sometimes called black mica as opposed to white mica – both form in some rocks, and in some instances side-by-side. Like other mica minerals, biotite has a perfect basal cleavage, and consists of flexible sheets, or lamellae. It has a crystal system, with tabular to prismatic crystals with an obvious pinacoid termination. It has four faces and two pinacoid faces to form a pseudohexagonal crystal. Although not easily seen because of the cleavage and sheets, fracture is uneven and it appears greenish to brown or black, and even yellow when weathered. It can be transparent to opaque, has a vitreous to pearly luster, when biotite is found in large chunks, they are called “books” because it resembles a book with pages of many sheets.
The color of biotite is usually black and the mineral has a hardness of 2. 5-3 on the Mohs scale of mineral hardness, biotite dissolves in both acid and alkaline aqueous solutions, with the highest dissolution rates at low pH. However, biotite dissolution is highly anisotropic with crystal edge surfaces reacting 45 to 132 times faster than basal surfaces, under cross-polarized light biotite can generally be identified by the gnarled birds eye extinction. Biotite is found in a variety of igneous and metamorphic rocks. For instance, biotite occurs in the lava of Mount Vesuvius, biotite in granite tends to be poorer in magnesium than the biotite found in its volcanic equivalent, rhyolite. Biotite is an essential phenocryst in some varieties of lamprophyre, biotite is occasionally found in large cleavable crystals, especially in pegmatite veins, as in New England and North Carolina. Other notable occurrences include Bancroft and Sudbury, Ontario and it is an essential constituent of many metamorphic schists, and it forms in suitable compositions over a wide range of pressure and temperature.
It has been estimated that biotite comprises up to 7% of the continental crust. The largest documented single crystals of biotite were approximately 7 m2 sheets found in Iveland, biotite is used extensively to constrain ages of rocks, by either potassium-argon dating or argon-argon dating. Because argon escapes readily from the crystal structure at high temperatures. Biotite is useful in assessing temperature histories of metamorphic rocks, because the partitioning of iron and magnesium between biotite and garnet is sensitive to temperature
Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate, about 10% of sedimentary rocks are limestones. The solubility of limestone in water and weak acid solutions leads to karst landscapes, most cave systems are through limestone bedrock. The first geologist to distinguish limestone from dolomite was Belsazar Hacquet in 1778, like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids and these organisms secrete shells made of aragonite or calcite, and leave these shells behind when they die. Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragment, some limestones do not consist of grains at all, and are formed completely by the chemical precipitation of calcite or aragonite, i. e. travertine.
Secondary calcite may be deposited by supersaturated meteoric waters and this produces speleothems, such as stalagmites and stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular appearance, the primary source of the calcite in limestone is most commonly marine organisms. Some of these organisms can construct mounds of rock known as reefs, below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone typically does not form in deeper waters. Limestones may form in lacustrine and evaporite depositional environments, calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, and dissolved ion concentrations. Calcite exhibits a characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases. Impurities will cause limestones to exhibit different colors, especially with weathered surfaces, Limestone may be crystalline, granular, or massive, depending on the method of formation.
Crystals of calcite, dolomite or barite may line small cavities in the rock, when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together, or it can fill fractures. Travertine is a banded, compact variety of limestone formed along streams, particularly there are waterfalls. Calcium carbonate is deposited where evaporation of the leaves a solution supersaturated with the chemical constituents of calcite. Tufa, a porous or cellular variety of travertine, is found near waterfalls, coquina is a poorly consolidated limestone composed of pieces of coral or shells. During regional metamorphism that occurs during the building process, limestone recrystallizes into marble
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west, the Irish Sea lies northwest of England and the Celtic Sea lies to the southwest. England is separated from continental Europe by the North Sea to the east, the country covers five-eighths of the island of Great Britain in its centre and south, and includes over 100 smaller islands such as the Isles of Scilly, and the Isle of Wight. England became a state in the 10th century, and since the Age of Discovery. The Industrial Revolution began in 18th-century England, transforming its society into the worlds first industrialised nation, Englands terrain mostly comprises low hills and plains, especially in central and southern England. However, there are uplands in the north and in the southwest, the capital is London, which is the largest metropolitan area in both the United Kingdom and the European Union. In 1801, Great Britain was united with the Kingdom of Ireland through another Act of Union to become the United Kingdom of Great Britain and Ireland.
In 1922 the Irish Free State seceded from the United Kingdom, leading to the latter being renamed the United Kingdom of Great Britain, the name England is derived from the Old English name Englaland, which means land of the Angles. The Angles were one of the Germanic tribes that settled in Great Britain during the Early Middle Ages, the Angles came from the Angeln peninsula in the Bay of Kiel area of the Baltic Sea. The earliest recorded use of the term, as Engla londe, is in the ninth century translation into Old English of Bedes Ecclesiastical History of the English People. According to the Oxford English Dictionary, its spelling was first used in 1538. The earliest attested reference to the Angles occurs in the 1st-century work by Tacitus, the etymology of the tribal name itself is disputed by scholars, it has been suggested that it derives from the shape of the Angeln peninsula, an angular shape. An alternative name for England is Albion, the name Albion originally referred to the entire island of Great Britain.
The nominally earliest record of the name appears in the Aristotelian Corpus, specifically the 4th century BC De Mundo, in it are two very large islands called Britannia, these are Albion and Ierne. But modern scholarly consensus ascribes De Mundo not to Aristotle but to Pseudo-Aristotle, the word Albion or insula Albionum has two possible origins. Albion is now applied to England in a poetic capacity. Another romantic name for England is Loegria, related to the Welsh word for England, the earliest known evidence of human presence in the area now known as England was that of Homo antecessor, dating to approximately 780,000 years ago. The oldest proto-human bones discovered in England date from 500,000 years ago, Modern humans are known to have inhabited the area during the Upper Paleolithic period, though permanent settlements were only established within the last 6,000 years
Basalt is a common extrusive igneous rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon. Flood basalt describes the formation in a series of basalt flows. By definition, basalt is an igneous rock with generally 45-55% silica and less than 10% feldspathoid by volume. Basalt commonly features a very fine-grained or glassy matrix interspersed with visible mineral grains, the average density is 3.0 gm/cm3. Basalt is defined by its content and texture, and physical descriptions without mineralogical context may be unreliable in some circumstances. Basalt is usually grey to black in colour, but rapidly weathers to brown or rust-red due to oxidation of its mafic minerals into hematite, although usually characterized as dark, basaltic rocks exhibit a wide range of shading due to regional geochemical processes. Due to weathering or high concentrations of plagioclase, some basalts can be quite light-coloured and these phenocrysts usually are of olivine or a calcium-rich plagioclase, which have the highest melting temperatures of the typical minerals that can crystallize from the melt.
Basalt with a texture is called vesicular basalt, when the bulk of the rock is mostly solid. Gabbro is often marketed commercially as black granite and these ultramafic volcanic rocks, with silica contents below 45% are usually classified as komatiites. Agricola applied basalt to the black rock of the Schloßberg at Stolpen. Tholeiitic basalt is relatively rich in silica and poor in sodium, included in this category are most basalts of the ocean floor, most large oceanic islands, and continental flood basalts such as the Columbia River Plateau. Basalt rocks are in some cases classified after their content in High-Ti and Low-Ti varieties. High-Ti and Low-Ti basalts have been distinguished in the Paraná and Etendeka traps and it has greater than 17% alumina and is intermediate in composition between tholeiite and alkali basalt, the relatively alumina-rich composition is based on rocks without phenocrysts of plagioclase. Alkali basalt is relatively poor in silica and rich in sodium and it is silica-undersaturated and may contain feldspathoids, alkali feldspar and phlogopite.
Boninite is a form of basalt that is erupted generally in back-arc basins. Ocean island basalt Lunar basalt On Earth, most basalt magmas have formed by melting of the mantle. Basalt commonly erupts on Io, the third largest moon of Jupiter, and has formed on the Moon, Venus. The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below, the mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate. The Mohs scale of hardness, based on scratch hardness comparison. Other polymorphs of calcium carbonate are the minerals aragonite and vaterite, aragonite will change to calcite at 380–470 °C, and vaterite is even less stable. Calcite is derived from the German Calcit, a term coined in the 19th century from the Latin word for lime and it is thus etymologically related to chalk. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms and it may occur as fibrous, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form and its fracture is conchoidal, but difficult to obtain. It has a defining Mohs hardness of 3, a gravity of 2.71.
Color is white or none, though shades of gray, orange, green, violet, calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence. A transparent variety called Iceland spar is used for optical purposes, acute scalenohedral crystals are sometimes referred to as dogtooth spar while the rhombohedral form is sometimes referred to as nailhead spar. Single calcite crystals display an optical property called birefringence and this strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect was first described by the Danish scientist Rasmus Bartholin in 1669, at a wavelength of ~590 nm calcite has ordinary and extraordinary refractive indices of 1.658 and 1.486, respectively. Between 190 and 1700 nm, the refractive index varies roughly between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4. Calcite, like most carbonates, will dissolve with most forms of acid, calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, and dissolved ion concentrations.
Although calcite is fairly insoluble in water, acidity can cause dissolution of calcite. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite, calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. On a landscape scale, continued dissolution of calcium carbonate-rich rocks can lead to the expansion and eventual collapse of cave systems, high-grade optical calcite was used in World War II for gun sights, specifically in bomb sights and anti-aircraft weaponry
Labradorite, a feldspar mineral, is an intermediate to calcic member of the plagioclase series. It has a percentage of between 50 and 70. The specific gravity ranges from 2.68 to 2.72, the streak is white, like most silicates. The refractive index ranges from 1.559 to 1.573, as with all plagioclase members, the crystal system is triclinic, and three directions of cleavage are present, two of which form nearly right angle prisms. It occurs as clear, white to gray, blocky to lath shaped grains in common mafic igneous rocks such as basalt and gabbro, the geological type area for labradorite is Pauls Island near the town of Nain in Labrador, Canada. It has reported in Norway and various other locations worldwide. Labradorite occurs in igneous rocks and is the feldspar variety most common in basalt. The uncommon anorthosite bodies are composed almost entirely of labradorite and it is found in metamorphic amphibolites and as a detrital component of some sediments. Common mineral associates in igneous rocks include olivine, amphiboles, Labradorite can display an iridescent optical effect known as labradorescence.
The term labradoresence was coined by Ove Balthasar Bøggild, who defined it as follows, Contributions to the understanding of the origin and cause of the effect were made by Rayleigh, the cause of this optical phenomenon is phase exsolution lamellar structure, occurring in the Bøggild miscibility gap. The effect is visible when the separation is between 128 to 252 nm, the lamellae are not necessarily parallel, and the lamellar structure is found to lack long range order. Relationships between lamellar separation and chemical composition have been found for the An content of the mineral, some gemstone varieties of labradorite exhibiting a high degree of labradorescence are called spectrolite. Aventurescence Larvikite Chisholm, Hugh, ed. Labradorite
In geology, a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. The term sill is synonymous with concordant intrusive sheet and this means that the sill does not cut across preexisting rocks, in contrast to dikes, discordant intrusive sheets which do cut across older rocks. Sills are fed by dikes, except in locations where they form in nearly vertical beds attached directly to a magma source. These planes or weakened areas allow the intrusion of a thin body of magma paralleling the existing bedding planes, concordant fracture zone. Sills parallel beds and foliations in the country rock. They can be emplaced in a horizontal orientation, although tectonic processes may cause subsequent rotation of horizontal sills into near vertical orientations. Sills can be confused with solidified lava flows, there are differences between them. Intruded sills will show partial melting and incorporation of the country rock.
On both contact surfaces of the rock into which the sill has intruded, evidence of heating will be observed. Lava flows will show this evidence only on the side of the flow. In addition, lava flows will show evidence of vesicles where gases escaped into the atmosphere. Because sills generally form at shallow depths below the surface, the pressure of overlying rock prevents this from happening much, lava flows will typically show evidence of weathering on their upper surface, whereas sills, if still covered by country rock, typically do not. Certain layered intrusions are a variety of sill that often contain important ore deposits, phanerozoic examples are usually smaller and include the Rùm peridotite complex of Scotland and the Skaergaard igneous complex of east Greenland. These intrusions often contain concentrations of gold, chromium, despite their concordant nature, many large sills change stratigraphic level within the intruded sequence, with each concordant part of the intrusion linked by relatively short dike-like segments.
Such sills are known as transgressive, examples include the Whin Sill, the geometry of large sill complexes in sedimentary basins has become clearer with the availability of 3D seismic reflection data. Such data has shown that many sills have a saucer shape. Sill may refer to the rise in depth near the mouth of a fjord caused by the moraine of the previous glacier. Sill swarm Batholith Stock Dike Laccolith Sheet intrusion