Open-pit mining
Open-pit, open-cast or open cut mining is a surface mining technique of extracting rock or minerals from the earth by their removal from an open pit or borrow. This form of mining differs from extractive methods that require tunnelling into the earth, such as long wall mining. Open-pit mines are used when deposits of commercially useful ore or rocks are found near the surface, it is applied to ore or rocks found at the surface because the overburden is thin or the material of interest is structurally unsuitable for tunnelling. In contrast, minerals that have been found underground but are difficult to retrieve due to hard rock, can be reached using a form of underground mining. To create an open-pit mine, the miners must determine the information of the ore, underground; this is done through drilling of probe holes in the ground plotting each hole location on a map. The information gained through the holes with provide an idea of the vertical extent of the ore's body; this vertical information is used to pit tentative locations of the benches that will occur in the mine.
It is important to consider the grade and economic value of the ore in the potential pit. Open-pit mines that produce building materials and dimension stone are referred to as "quarries." Open-pit mines are enlarged until either the mineral resource is exhausted, or an increasing ratio of overburden to ore makes further mining uneconomic. When this occurs, the exhausted mines are sometimes converted to landfills for disposal of solid wastes. However, some form of water control is required to keep the mine pit from becoming a lake, if the mine is situated in a climate of considerable precipitation or if any layers of the pit forming the mine border productive aquifers. Open-pit mining is to be considered one of the most dangerous sectors in the industrial world, it causes significant effects to miners health, as well as damage to the ecological land. Open-pit mining causes changes to vegetation and bedrock, which contributes to changes in surface hydrology, groundwater levels, flow paths. Additionally, open-pit produces harmful pollutants depending on the type of mineral being mined, the type of mining process being used.
Open-cast mines are dug on benches. The interval of the benches depends on the deposit being mined, the mineral being mined, the size of the machinery, being used. Large mine benches are 12 to 15 metres thick. In contrast, many quarries do not use benches, as they are shallow. Mining can be conducted on more than one bench at a time, access to different benches is done with a system of ramps; the width of each bench is determined by the size of the equipment being used 20-40 metres wide. Downward ramps are created to allow mining on a new level to begin; this new level will become progressively wider to form the new pit bottom. Most walls of the pit are mined on an angle less than vertical. Waste rock is stripped when the pit becomes deeper, therefore this angle is a safety precaution to prevent and minimize damage and danger from rock falls. However, this depends on how weathered and eroded the rocks are, the type of rocks involved, it depends on the amount of structural weaknesses occur within the rocks, such as a faults, joints or foliations.
The walls are stepped. The inclined section of the wall is known as the batter, the flat part of the step is known as the bench or berm; the steps in the walls help prevent. In some instances additional ground support is required and rock bolts, cable bolts and shotcrete are used. De-watering bores may be used to relieve water pressure by drilling horizontally into the wall, enough to cause failures in the wall by itself. A haul road is situated at the side of the pit, forming a ramp up which trucks can drive, carrying ore and waste rock. Open-pit mines create a significant amount of waste. One million tons of ore and waste rock can move from the largest mines per day, a couple thousand tons moved from small mines per day. There is four main operations in a mine that contribute to this load: drilling, blasting and hauling. Waste rock is hauled to a waste dump. Waste dumps can be piled at the surface of the active pit, or in mined pits. Leftover waste from processing the ore is called tailings, is in the form of a slurry.
This is pumped to a tailings settling pond, where the water is reused or evaporated. Tailings dams can be toxic due to the presence of unextracted sulfide minerals, some forms of toxic minerals in the gangue, cyanide, used to treat gold ore via the cyanide leach process. If proper environmental protections are not in place, this toxicity can harm the surrounding environment. Open-pit mining involves the process of disrupting the ground, which leads to the creation of air pollutants; the main source of air pollutants comes from the transportation of minerals, but their are various other factors including drilling and the loading and unloading of overburden. These type of pollutants cause significant damage to public health and safety in addition to damaging the air quality; the inhalation of these pollutants can cause issues to the lungs and increase mortality. Furthermore, the pollutants affect fauna in the areas surrounding open-pit mines. Open-pit gold mining is one of the highest potential mining threats on the environment as it affects the air and water chemistry.
The exposed dust may be toxic or radioactive, making it a health concern for the workers and the surrounding communities. A form of open-
Carnegie Institution for Science
The Carnegie Institution of Washington, known for public purposes as the Carnegie Institution for Science, is an organization in the United States established to fund and perform scientific research. The institution is headquartered in Washington, D. C. Beginning during 1895, Andrew Carnegie donated his vast fortune to establish over 20 organizations around the world that now feature his surname and perform work involving topics as diverse as art, international affairs, world peace, scientific research; the organizations are related by name only. In 2007, the institution adopted the public name "Carnegie Institution for Science" to distinguish itself better from other organizations established by and named for Andrew Carnegie; the institution remains and the Carnegie Institution of Washington, but now has a public identity that describes its work more precisely. "It is proposed to found in the city of Washington, an institution which...shall in the broadest and most liberal manner encourage investigation and discovery show the application of knowledge to the improvement of mankind..."
— Andrew Carnegie, January 28, 1902 Beginning during 1895, Andrew Carnegie contributed his vast fortune toward the establishment of 22 organizations that presently feature his surname and perform work in such topics as art, international affairs and scientific research. During 1901, Andrew Carnegie retired from business to begin his career in philanthropy. Among his new enterprises, he considered establishing a national university in Washington, D. C. similar to the great centers of learning in Europe. Because he was concerned that a new university could weaken existing universities, he opted for an independent research organization that would increase basic scientific knowledge. Carnegie communicated with President Theodore Roosevelt and declared his readiness to endow the new institution with $10 million, he added $2 million more to the endowment during 1907, another $10 million during 1911. By some estimates, the value of his endowment in current terms was $500 million; as ex officio members of the first board of trustees, Carnegie chose the President of the United States, the President of the Senate, the Speaker of the House of Representatives, the secretary of the Smithsonian Institution and the president of the National Academy of Sciences.
In all, he selected 27 men for the institution's original board. Their first meeting was held in the office of the Secretary of State on January 29, 1902, Daniel Coit Gilman, president of Johns Hopkins University, was elected president; the institution was incorporated by the U. S. Congress during 1903; the president and trustees devoted much of the institution's budget to individual grants for various topics, including astronomy, literature, economics and mathematics. Among the researchers who received individual grants were American physicist Albert A. Michelson, paleontologist Oliver Perry Hay, botanist Janet Russell Perkins, Thomas Hunt Morgan and his "fly group", geologist Thomas Chrowder Chamberlin, historian of science George Sarton, rocket pioneer Robert H. Goddard and botanist Luther Burbank; the institution funded archaeological research by Sylvanus Morley at Chichen Itza. As directed by Robert Woodward, who became president during 1904, the board changed its practice, deciding to provide major funding to departments of research rather than to individuals.
This allowed them to concentrate on fewer topics and fund groups of researchers in related areas over many years. Starting in 1907 the Institution maintained the Tortugas Laboratory on Garden Key, under the direction of Alfred G. Mayer. Since the beginning, the Carnegie Institution has made discoveries but left the development to others; this philosophy has resulted in unexpected results, including the development of hybrid corn, the technology that led to Pyrex ® glass, novel techniques to control genes known as RNA interference. Some of Carnegie's researchers from the early and middle years of the 20th century are well known: Edwin Hubble, who revolutionized astronomy with his discovery that the universe is expanding and that there are galaxies other than our own Milky WayCharles Richter, who created the earthquake measurement scale; when the United States joined World War II, Vannevar Bush was president of the Carnegie Institution. Several months before, on June 12, 1940, Bush had been instrumental in persuading President Franklin Roosevelt to create the National Defense Research Committee to mobilize and coordinate the nation's scientific war effort.
Bush housed the new agency in the Carnegie Institution's administrative headquarters at 16th and P Streets, NW, in Washington, DC, converting its great rotunda and auditorium into office cubicles. From this location, Bush supervised, among the Manhattan Project. Further, Carnegie scientists cooperated with the development of the proximity fuze and mass production of penicillin; as of June 30, 2014, the Institution's endowment was valued at $980 million. Expenses for scientific programs and administration was
Encyclopædia Britannica
The Encyclopædia Britannica published by Encyclopædia Britannica, Inc. is a general knowledge English-language encyclopaedia. It was written by more than 4,000 contributors; the 2010 version of the 15th edition, which spans 32 volumes and 32,640 pages, was the last printed edition. The Britannica is the English-language encyclopaedia/encyclopedia, in print for the longest time: it lasted 244 years, it was first published between 1768 and 1771 as three volumes. The encyclopaedia grew in size: the second edition was 10 volumes, by its fourth edition it had expanded to 20 volumes, its rising stature as a scholarly work helped recruit eminent contributors, the 9th and 11th editions are landmark encyclopaedias for scholarship and literary style. Beginning with the 11th edition and following its acquisition by an American firm, the Britannica shortened and simplified articles to broaden its appeal to the North American market. In 1933, the Britannica became the first encyclopaedia to adopt "continuous revision", in which the encyclopaedia is continually reprinted, with every article updated on a schedule.
In March 2012, Encyclopædia Britannica, Inc. announced it would no longer publish printed editions, would focus instead on Encyclopædia Britannica Online. The 15th edition had a three-part structure: a 12-volume Micropædia of short articles, a 17-volume Macropædia of long articles, a single Propædia volume to give a hierarchical outline of knowledge; the Micropædia was meant as a guide to the Macropædia. Over 70 years, the size of the Britannica has remained steady, with about 40 million words on half a million topics. Though published in the United States since 1901, the Britannica has for the most part maintained British English spelling. Since 1985, the Britannica has had four parts: the Micropædia, the Macropædia, the Propædia, a two-volume index; the Britannica's articles are found in the Micro- and Macropædia, which encompass 12 and 17 volumes each volume having one thousand pages. The 2007 Macropædia has 699 in-depth articles, ranging in length from 2 to 310 pages and having references and named contributors.
In contrast, the 2007 Micropædia has 65,000 articles, the vast majority of which contain fewer than 750 words, no references, no named contributors. The Micropædia articles are intended for quick fact-checking and to help in finding more thorough information in the Macropædia; the Macropædia articles are meant both as authoritative, well-written articles on their subjects and as storehouses of information not covered elsewhere. The longest article is on the United States, resulted from the merger of the articles on the individual states; the 2013 edition of Britannica contained forty thousand articles. Information can be found in the Britannica by following the cross-references in the Micropædia and Macropædia. Hence, readers are recommended to consult instead the alphabetical index or the Propædia, which organizes the Britannica's contents by topic; the core of the Propædia is its "Outline of Knowledge", which aims to provide a logical framework for all human knowledge. Accordingly, the Outline is consulted by the Britannica's editors to decide which articles should be included in the Micro- and Macropædia.
The Outline is intended to be a study guide, to put subjects in their proper perspective, to suggest a series of Britannica articles for the student wishing to learn a topic in depth. However, libraries have found that it is scarcely used, reviewers have recommended that it be dropped from the encyclopaedia; the Propædia has color transparencies of human anatomy and several appendices listing the staff members and contributors to all three parts of the Britannica. Taken together, the Micropædia and Macropædia comprise 40 million words and 24,000 images; the two-volume index has 2,350 pages, listing the 228,274 topics covered in the Britannica, together with 474,675 subentries under those topics. The Britannica prefers British spelling over American. However, there are exceptions such as defense rather than defence. Common alternative spellings are provided with cross-references such as "Color: see Colour." Since 1936, the articles of the Britannica have been revised on a regular schedule, with at least 10% of them considered for revision each year.
According to one Britannica website, 46% of its articles were revised over the past three years. The alphabetization of articles in the Micropædia and Macropædia follows strict rules. Diacritical marks and non-English letters are ignored, while numerical entries such as "1812, War of" are alphabetized as if the number had been written out. Articles with identical names are ordered first by persons by places by things. Rulers with identical names are organized first alphabetically by country and by chronology. Places that share names are
Bloemfontein
Bloemfontein is the capital city of the province of Free State of South Africa. Situated at an altitude of 1,395 m above sea level, the city is home to 520,000 residents and forms part of the Mangaung Metropolitan Municipality which has a population of 747,431; the city of Bloemfontein hosts the Supreme Court of Appeal of South Africa, the Franklin Game Reserve, Naval Hill, the Maselspoort Resort and the Sand du Plessis Theatre. The city hosts numerous museums, including the National Women's Monument, the Anglo-Boer War Museum, the National Museum, the Oliewenhuis Art Museum Bloemfontein host sub-Saharan Africa's first digital planetarium, the Naval Hill Planetarium and Boyden Observatory, an astronomical research observatory erected by Harvard University. Bloemfontein is popularly and poetically known as "the city of roses", for its abundance of these flowers and the annual rose festival held there; the city's Sesotho name is Mangaung, meaning "place of cheetahs". The origin of the city's name is disputed.
It is borrowed from the Dutch words bloem and fontein, meaning fountain of flowers. Popular legends include an ox named "Bloem" owned by Rudolphus Martinus Brits, one of the pioneer farmers, taken by a lion near a fountain on his property, while another story names Jan Bloem, a Korana KhoiKhoi leader who settled there. Though a predominantly Afrikaner settlement, Bloemfontein was founded in 1846 as a fort by British army major Henry Douglas Warden as a British outpost in the Transoranje region, at that stage occupied by various groups of peoples including Cape Colony Trek Boers and Barolong. Warden chose the site because of its proximity to the main route to Winburg, the spacious open country, the absence of horse sickness. Bloemfontein was the original farm of Johannes Nicolaas Brits born 21 February 1790, owner and first inhabitant of Bloemfontein. Johann – as he was known – sold the farm to Major Warden. With colonial policy shifts, the region changed into the Orange River Sovereignty and the Orange Free State Republic.
From 1902–10 it served as the capital of the Orange River Colony and since that time as the provincial capital of the Free State. In 1910 it became the Judicial capital of the Union of South Africa The Orange Free State was an independent Boer sovereign republic in southern Africa during the second half of the 19th century. Extending between the Orange and Vaal rivers, its borders were determined by the United Kingdom of Great Britain and Ireland in 1848 when the region was proclaimed as the Orange River Sovereignty, with a seat of a British Resident in Bloemfontein; as the capital of the Orange Free State Republic the growth and maturing of the Republic resulted in the growth of Bloemfontein. Numerous public buildings that remain in use today were constructed; this was facilitated by the excellent governance of the Republic and the compensation from the British for the loss of the diamond rich Griqualand area. The old Orange Free State's presidential residence the Old Presidency is a museum and cultural space in the city.
A railway line was built in 1890 connecting Bloemfontein to Cape Town. The writer J. R. R. Tolkien was born in the city on 3 January 1892, though his family left South Africa following the death of his father, Arthur Tolkien, while Tolkien was only three, he recorded that his earliest memories were of "a hot country". In 1899 the city was the site of the Bloemfontein Conference, which failed to prevent the outbreak of the Second Boer War; the conference was a final attempt to avert a war between the South African Republic. With its failure the stage was set for war, which broke out on 11 October 1899; the rail line from Cape Town provided a centrally located railway station, proved critical to the British in occupying the city later. On 13 March 1900, following the Battle of Paardeberg, British forces captured the city and built a concentration camp nearby to house Boer women and children; the National Women's Monument, on the outskirts of the city, pays homage to the 26,370 women and children as well as 1,421 old men who died in these camps in various parts of the country.
The hill in town was named Naval Hill after the naval guns brought in by the British in order to fortify the position against attack. On 31 May 1910 eight years after the Boers signed the Peace Treaty of Vereeniging that ended the Anglo-Boer War between the British Empire and two Boer states, the South African Republic and the Orange Free State, South Africa became a Union. Due to disagreements over where the Union's capital should be, a compromise was reached that allowed Bloemfontein to host Appellate Division and become the Union's judicial capital. Bloemfontein was given financial compensation. On 8 January 1912, the South African Native National Congress was founded in Bloemfontein; the Union of South Africa had not granted rights to black South Africans, causing the organisation's creation. Its primary aim was to fight for the rights of black South Africans. From 1 to 9 January 1914, James Barry Munnik Hertzog and his supporters met in Bloemfontein to form the National Party of the Orange Free State, to
Great Depression
The Great Depression was a severe worldwide economic depression that took place during the 1930s, beginning in the United States. The timing of the Great Depression varied across nations, it was the longest and most widespread depression of the 20th century. In the 21st century, the Great Depression is used as an example of how intensely the world's economy can decline; the Great Depression started in the United States after a major fall in stock prices that began around September 4, 1929, became worldwide news with the stock market crash of October 29, 1929. Between 1929 and 1932, worldwide gross domestic product fell by an estimated 15%. By comparison, worldwide GDP fell by less than 1% from 2008 to 2009 during the Great Recession; some economies started to recover by the mid-1930s. However, in many countries the negative effects of the Great Depression lasted until the beginning of World War II; the Great Depression had devastating effects in countries both poor. Personal income, tax revenue and prices dropped, while international trade plunged by more than 50%.
Unemployment in the U. S. rose to 25% and in some countries rose as high as 33%. Cities around the world were hit hard those dependent on heavy industry. Construction was halted in many countries. Farming communities and rural areas suffered as crop prices fell by about 60%. Facing plummeting demand with few alternative sources of jobs, areas dependent on primary sector industries such as mining and logging suffered the most. Economic historians attribute the start of the Great Depression to the sudden devastating collapse of U. S. stock market prices on October 29, 1929, known as Black Tuesday. However, some dispute this conclusion and see the stock crash as a symptom, rather than a cause, of the Great Depression. After the Wall Street Crash of 1929 optimism persisted for some time. John D. Rockefeller said "These are days. In the 93 years of my life, depressions have gone. Prosperity has always returned and will again." The stock market turned upward in early 1930. This was still 30% below the peak of September 1929.
Together and business spent more in the first half of 1930 than in the corresponding period of the previous year. On the other hand, many of whom had suffered severe losses in the stock market the previous year, cut back their expenditures by 10%. In addition, beginning in the mid-1930s, a severe drought ravaged the agricultural heartland of the U. S. By mid-1930, interest rates had dropped to low levels, but expected deflation and the continuing reluctance of people to borrow meant that consumer spending and investment were depressed. By May 1930, automobile sales had declined to below the levels of 1928. Prices in general began to decline, although wages held steady in 1930. A deflationary spiral started in 1931. Farmers faced a worse outlook. At its peak, the Great Depression saw nearly 10% of all Great Plains farms change hands despite federal assistance; the decline in the U. S. economy was the factor. Frantic attempts to shore up the economies of individual nations through protectionist policies, such as the 1930 U.
S. Smoot–Hawley Tariff Act and retaliatory tariffs in other countries, exacerbated the collapse in global trade. By 1933, the economic decline had pushed world trade to one-third of its level just four years earlier. Change in economic indicators 1929–32 The two classical competing theories of the Great Depression are the Keynesian and the monetarist explanation. There are various heterodox theories that downplay or reject the explanations of the Keynesians and monetarists; the consensus among demand-driven theories is that a large-scale loss of confidence led to a sudden reduction in consumption and investment spending. Once panic and deflation set in, many people believed they could avoid further losses by keeping clear of the markets. Holding money became profitable as prices dropped lower and a given amount of money bought more goods, exacerbating the drop in demand. Monetarists believe that the Great Depression started as an ordinary recession, but the shrinking of the money supply exacerbated the economic situation, causing a recession to descend into the Great Depression.
Economists and economic historians are evenly split as to whether the traditional monetary explanation that monetary forces were the primary cause of the Great Depression is right, or the traditional Keynesian explanation that a fall in autonomous spending investment, is the primary explanation for the onset of the Great Depression. Today the controversy is of lesser importance since there is mainstream support for the debt deflation theory and the expectations hypothesis that building on the monetary explanation of Milton Friedman and Anna Schwartz add non-monetary explanations. There is consensus that the Federal Reserve System should have cut short the process of monetary deflation and banking collapse. If they had done this, the economic downturn would have been much shorter. British economist John Maynard Keynes argued in The General Theory of Employment and Money that lower aggregate expenditures in the economy contributed to a massive decline in income and to employment, well below the average.
In such a situation, the economy reached equilibrium at low levels of economic activity and high unemployment. Keynes' basic idea was simple
Underground mining (hard rock)
Underground hard rock mining refers to various underground mining techniques used to excavate hard minerals those containing metals such as ore containing gold, iron, zinc, nickel and lead, but involves using the same techniques for excavating ores of gems such as diamonds or rubies. Soft rock mining refers to excavation of softer minerals such as coal, or oil sands. Accessing underground ore can be achieved via a decline, inclined vertical shaft or adit. Declines can be a spiral tunnel which circles either the flank of the deposit or circles around the deposit; the decline begins with a box cut, the portal to the surface. Depending on the amount of overburden and quality of bedrock, a galvanized steel culvert may be required for safety purposes, they may be started into the wall of an open cut mine. Shafts are vertical excavations sunk adjacent to an ore body. Shafts are sunk for ore bodies. Shaft haulage is more economical than truck haulage at depth, a mine may have both a decline and a ramp.
Adits are horizontal excavations into the side of a mountain. Adits are used for horizontal or near-horizontal ore bodies where there is no need for a ramp or shaft. Declines are started from the side of the high wall of an open cut mine when the ore body is of a payable grade sufficient to support an underground mining operation, but the strip ratio has become too great to support open cast extraction methods, they are often built and maintained as an emergency safety access from the underground workings and a means of moving large equipment to the workings. Levels are shaft to access the ore body. Stopes are excavated perpendicular to the level into the ore. There are two principal phases of underground mining: development production mining. Development mining is composed of excavation entirely in waste rock in order to gain access to the orebody. There are six steps in development mining: remove blasted material, installing support or/and reinforcement using shotcrete etceteras, drill face rock, load explosives, blast explosives.
To start the mining, the first step is to make the path to go down. The path is defined. Before the start of Decline all preplanning of Power facility, drilling arrangement, ventilation and, muck withdrawal facilities are required. Production mining is further broken down into long hole and short hole. Short hole mining is similar to development mining. There are several different methods of long hole mining. Long hole mining requires two excavations within the ore at different elevations below surface. Holes are loaded with explosives; the holes are blasted and the ore is removed from the bottom excavation. One of the most important aspects of underground hard rock mining is ventilation. Ventilation is the primary method of clearing hazardous gases and/or dust which are created from drilling and blasting activity, diesel equipment, or to protect against gases that are emanating from the rock. Ventilation is used to manage underground temperatures for the workers. In deep, hot mines ventilation is used to cool the workplace.
Ventilation raises are used to transfer ventilation from surface to the workplaces, can be modified for use as emergency escape routes. The primary sources of heat in underground hard rock mines are virgin rock temperature, auto compression, fissure water. Other small contributing factors are blasting; some means of support is required in order to maintain the stability of the openings that are excavated. This support comes in two forms. Area ground support is used to prevent major ground failure. Holes are drilled into the back and walls and a long steel rod is installed to hold the ground together. There are three categories of rock bolt, differentiated by, they are: Point anchor bolts are a common style of area ground support. A point anchor bolt is a metal bar between 20 mm – 25 mm in diameter, between 1 m – 4 m long. There is an expansion shell at the end of the bolt, inserted into the hole; as the bolt is tightened by the installation drill the expansion shell expands and the bolt tightens holding the rock together.
Mechanical bolts are considered temporary support as their lifespan is reduced by corrosion as they are not grouted. Resin grouted; the rebar used does not have an expansion shell. Once the hole for the rebar is drilled, cartridges of polyester resin are installed in the hole; the rebar bolt is spun by the installation drill. This mixes it. Once the resin hardens, the drill spinning tightens the rebar bolt holding the rock together. Resin grouted. Cable bolts are used around large excavations. Cable bolts are much larger than standard
Xenolith
A xenolith is a rock fragment that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term xenolith is exclusively used to describe inclusions in igneous rock during magma emplacement and eruption. Xenoliths may be engulfed along the margins of a magma chamber, torn loose from the walls of an erupting lava conduit or explosive diatreme or picked up along the base of a flowing body of lava on the Earth's surface. A xenocryst is an individual foreign crystal included within an igneous body. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes. Xenoliths can be non-uniform within individual locations in areas which are spatially limited, e.g. rhyolite-dominated lava of Niijima volcano contains two types of gabbroic xenoliths which are of different origin - they were formed in different temperature and pressure conditions. Although the term xenolith is most associated with igneous inclusions, a broad definition could include rock fragments which have become encased in sedimentary rock.
Xenoliths have been found in some meteorites. To be considered a true xenolith, the included rock must be identifiably different from the rock in which it is enveloped. Xenoliths and xenocrysts provide important information about the composition of the otherwise inaccessible mantle. Basalts, kimberlites and lamprophyres, which have their source in the upper mantle contain fragments and crystals assumed to be a part of the originating mantle mineralogy. Xenoliths of dunite and spinel lherzolite in basaltic lava flows are one example. Kimberlites contain, in addition to diamond xenocrysts, fragments of lherzolites of varying composition; the aluminium-bearing minerals of these fragments provide clues to the depth of origin. Calcic plagioclase is stable to a depth of 25 km. Between 25 km and about 60 km, spinel is the stable aluminium phase. At depths greater than about 60 km, dense garnet becomes the aluminium-bearing mineral; some kimberlites contain xenoliths of eclogite, considered to be the high-pressure metamorphic product of basaltic oceanic crust, as it descends into the mantle along subduction zones.
The large-scale inclusion of foreign rock strata at the margins of an igneous intrusion is called a roof pendant. Nixon, Peter H.. Mantle Xenoliths. J. Wiley & Sons. ISBN 0-471-91209-3
