The Hoba or Hoba West meteorite lies on the farm Hoba West, not far from Grootfontein, in the Otjozondjupa Region of Namibia. It has been uncovered but, because of its mass, has never been moved from where it fell. The main mass is estimated at more than 60 tons, making it the largest known meteorite and it is the most massive naturally occurring piece of iron known on Earths surface. The Hoba meteorite impact is thought to have occurred more recently than 80,000 years ago and it is inferred that the Earths atmosphere slowed the object to the point that it impacted the surface at terminal velocity, thereby remaining intact and causing little excavation. The meteorite is unusual in that it is flat on both surfaces, possibly causing it to have skipped across the top of the atmosphere like a flat stone skipping on water. The Hoba meteorite left no preserved crater and its discovery was a chance event, the owner of the land, Jacobus Hermanus Brits, encountered the object while ploughing one of his fields with an ox.
During this task, he heard a loud metallic scratching sound, the obstruction was excavated, identified as a meteorite and described by Mr. Brits, whose report was published in 1920 and can be viewed at the Grootfontein Museum in Namibia. Friedrich Wilhelm Kegel took the first published photograph of the Hoba meteorite, Hoba is a tabloid body of metal, measuring 2. 7×2. 7×0.9 metres. In 1920 its mass was estimated at 66 tons, scientific sampling and vandalism reduced its bulk over the years. The remaining mass is estimated at just over 60 tons, the meteorite is composed of about 84% iron and 16% nickel, with traces of cobalt. It is classified as an iron meteorite belonging to the nickel-rich chemical class IVB. A crust of iron hydroxides is locally present on the surface, in 1985 Rössing Uranium Ltd. made resources and funds available to the Namibian government to provide additional protection against vandalism. In 1987 Mr. J. Engelbrecht, the owner of Hoba West farm, donated the meteorite, that year the government opened a tourist centre at the site.
As a result of developments, vandalism of the Hoba meteorite has ceased. Glossary of meteoritics Universe, The Definitive Visual Dictionary, Robert Dinwiddie, DK Adult Publishing, pg.223. P. E. Spargo, The History of the Hoba Meteorite Part I, Nature and Discovery, Monthly Notes of the Astronomical Society of Southern Africa 67, nos. 5/6, pp. 85–94. P. E. Spargo, The History of the Hoba Meteorite Part II, The News Spreads, Monthly Notes of the Astronomical Society of Southern Africa 67, nos. 9/10, pp. 166–77. P. E. Spargo, The History of the Hoba Meteorite Part III, Known and Loved by All, Monthly Notes of the Astronomical Society of Southern Africa 67, full text at The Free Library
The Sahara is the largest hot desert and the third largest desert in the world after Antarctica and the Arctic. Its area of 9,200,000 square kilometres is comparable to the area of the United States. The desert comprises much of North Africa, excluding the fertile region on the Mediterranean Sea coast, the Atlas Mountains of the Maghreb, and the Nile Valley in Egypt and Sudan. It stretches from the Red Sea in the east and the Mediterranean in the north to the Atlantic Ocean in the west, where the landscape gradually changes from desert to coastal plains. To the south, it is bounded by the Sahel, a belt of tropical savanna around the Niger River valley. The Sahara can be divided into several regions including, the western Sahara, the central Ahaggar Mountains, the Tibesti Mountains, the Aïr Mountains, the Ténéré desert, the name Sahara is derived from ṣaḥārā, the plural of the Arabic word for desert. The Sahara covers large parts of Algeria, Egypt, Mali, Morocco, Western Sahara, Sudan and it covers 9 million square kilometres, amounting to 31% of Africa.
If all areas with an annual precipitation of less than 250 mm were included. It is one of three physiographic provinces of the African massive physiographic division. The Sahara is mainly rocky hamada, Ergs form only a minor part, wind or rare rainfall shape the desert features, sand dunes, dune fields, sand seas, stone plateaus, gravel plains, dry valleys, dry lakes, and salt flats. Unusual landforms include the Richat Structure in Mauritania, several deeply dissected mountains, many volcanic, rise from the desert, including the Aïr Mountains, Ahaggar Mountains, Saharan Atlas, Tibesti Mountains, Adrar des Iforas, and the Red Sea hills. The highest peak in the Sahara is Emi Koussi, a volcano in the Tibesti range of northern Chad. The central Sahara is hyperarid, with sparse vegetation, the northern and southern reaches of the desert, along with the highlands, have areas of sparse grassland and desert shrub, with trees and taller shrubs in wadis, where moisture collects. In the central, hyperarid region, there are subdivisions of the great desert, the Ténéré, the Libyan Desert, the Eastern Desert.
These extremely arid areas often receive no rain for years, the northern limit corresponds to the 100 mm isohyet of annual precipitation. To the south, the Sahara is bounded by the Sahel, the southern limit of the Sahara is indicated botanically by the southern limit of Cornulaca monacantha, or northern limit of Cenchrus biflorus, a grass typical of the Sahel. According to climatic criteria, the limit of the Sahara corresponds to the 150 mm isohyet of annual precipitation. The Sahara is the worlds largest low-latitude hot desert and this steady descending airflow causes a warming and a drying effect in the upper troposphere
Hexahedrites are a structural class of iron meteorite. They are composed almost exclusively of the nickel-iron alloy kamacite and are lower in nickel content than the octahedrites, the nickel concentration in hexahedrites is always below 5. 8% and only rarely below 5. 3%. The name comes from the structure of the kamacite crystal. These lines are named after Johann G. Neumann, who discovered them in 1848, concentrations of trace elements are used to separate the iron meteorites into chemical classes, which correspond to separate asteroid parent bodies. Chemical classes that include hexahedrites are, IIAB meteorites IIG meteorites Glossary of meteoritics
Cape York meteorite
The Cape York meteorite is named for Cape York, near the location of its discovery in Savissivik, Meteorite Island, and is one of the largest iron meteorites in the world. The meteorite collided with Earth nearly 10,000 years ago, the iron masses were known to Inuit as Ahnighito, weighing 31 metric tons, the Woman, weighing 3 metric tons, and the Dog, weighing 400 kilograms. For centuries, Inuit living near the meteorites used them as a source of metal for tools, the Inuit would work the metal using cold forging—that is, by stamping and hammering it. The first stories of its existence reached scientific circles in 1818, five expeditions between 1818 and 1883 failed to find the source of the iron. It was located in 1894 by Robert E. Peary, the famous American Navy Arctic explorer, Peary enlisted the help of a local Inuit guide, who brought him to Saviksoah Island, just off northern Greenlands Cape York in 1894. It took Peary three years to arrange and carry out the loading of the iron meteorites onto ships.
It required the building of Greenlands only railroad, Peary sold the pieces for $40,000 to the American Museum of Natural History in New York City where they are still on display. Today the 3.4 m x 2.1 m x 1.7 m piece named Ahnighito is open for viewing at the American Museum of Natural History in the Arthur Ross Hall and it is the heaviest meteorite that has ever been relocated. It is so heavy that it was necessary to build its display stand so that the supports reached directly to the bedrock below the museum, in 1963, a fourth major piece of the Cape York meteorite was discovered by Vagn F. Buchwald on Agpalilik peninsula. The Agpalilik meteorite, known as the Man, weighs about 20 metric tons, there are abundant elongated troilite nodules. The troilite nodules contain inclusions of chromite, phosphates, the rare nitride mineral carlsbergite occurs within the matrix of the metal phase. Graphite was not observed and the isotopes are in disequilibrium. Glossary of meteoritics History of ferrous metallurgy Archaeometallurgy Inuit culture Patricia A. M.
Huntington, Robert E Peary and the Cape York meteorites American Museum of Natural History www. meteoritestudies. com Cape York on the Meteoritical Bulletin Database
The ultimate goal of meteorite classification is to group all meteorite specimens that share a common origin on a single, identifiable parent body. This could be a planet, Moon, or other current Solar System object, as such information comes to light, the classification system will most likely evolve. Beyond the assignment of meteorites into groups, which essentially universally accepted and it is fairly common for groups that seem to be closely related to be referred to as clans. In turn, groups or clans that appear to be loosely related are often referred to as chondrite classes, but higher order terms for aggregating groups of meteorites tend to be somewhat chaotic in the scientific and popular literature. There is little agreement on how to fit nonchondritic meteorite groups into an overall scheme, several other classification terms are in widespread use, Type, a historic top level of classification that grouped all meteorites into one of four types, achondrite, iron or stony-iron. Anomalous, meteorites that are members of well-established groups that are different enough in some important property to merit distinction from the other members, grouplet, a provisional group with less than 5 members.
Duo, a group with only 2 members. Ungrouped, meteorites that do not fit any known group, though they may fit into a clan or class, meteorites are often divided into three overall categories based on whether they are dominantly composed of rocky material, metallic material, or mixtures. These categories have been in use since at least the early 19th century but do not have much significance, they are simply a traditional. In fact, the term stony iron is a misnomer as currently used, one group of chondrites has over 50% metal by volume and contains meteorites that were called stony irons until their affinities with chondrites were recognized. Some iron meteorites contain silicate inclusions but are rarely described as stony irons. Nevertheless, these three categories sit at the top of the most widely used classification system. Stony meteorites are divided into two other categories and achondrites. Stony–iron meteorites have always been divided into pallasites and mesosiderites. g, E. Rubin classification scheme, Two alternative general classification schemes were recently published, illustrating the lack of consensus on how to classify meteorites beyond the level of groups.
In the Krot et al. scheme the following hierarchy is used, modern meteorite classification was worked out in the 1860s, based on Gustav Roses and Nevil Story Maskelynes classifications. Gustav Rose worked on the collection of the Museum für Naturkunde and Maskelyne on the collection of the British Museum. Rose was the first to make different categories for meteorites with chondrules, story-Maskelyne differentiated between siderites and aerolites. In 1872 Gustav Tschermak published his first meteorite classification based on Gustav Roses catalog from 1864, further modifications were made by Aristides Brezina
Ataxites are a structural class of iron meteorites with a high nickel content and show no Widmanstätten patterns upon etching. Ataxites are composed mainly of iron, a native metal found in meteorites that consists of the mineral taenite with minor amounts of plessite, troilite. Ataxites are the most nickel-rich meteorites known, they contain over 18% nickel. Most ataxites belong to the IVB group or are classified as Iron, some ataxites belong to the IAB group and fall into the sHL, sLH, sHH and ung subgroup. Only a couple of ataxites have been classified into the IAB complex and they are a rare class, with none of the about 50 observed iron meteorite falls being an ataxite, the largest meteorite ever, the Hoba meteorite, belongs to this class. A Tibetan Buddhist statue, the Iron Man, was carved from an ataxite meteorite. It might even be made from a fragment of the Chinga meteorite, other examples of ataxites are the Dronino meteorite and pieces of the Gebel Kamil
Germanium is a chemical element with symbol Ge and atomic number 32. It is a lustrous, grayish-white metalloid in the group, chemically similar to its group neighbors tin. Pure germanium is a semiconductor with a similar to elemental silicon. Like silicon, germanium naturally reacts and forms complexes with oxygen in nature, unlike silicon, it is too reactive to be found naturally on Earth in the free state. Because it seldom appears in high concentration, germanium was discovered late in the history of chemistry. Germanium ranks near fiftieth in relative abundance of the elements in the Earths crust, in 1869, Dmitri Mendeleev predicted its existence and some of its properties from its position on his periodic table, and called the element ekasilicon. Nearly two decades later, in 1886, Clemens Winkler found the new element along with silver and sulfur, although the new element somewhat resembled arsenic and antimony in appearance, the combining ratios in compounds agreed with Mendeleevs predictions for a relative of silicon.
Winkler named the element after his country, today, germanium is mined primarily from sphalerite, though germanium is recovered commercially from silver and copper ores. Germanium metal is used as a semiconductor in transistors and various electronic devices. Historically, the first decade of semiconductor electronics was based entirely on germanium, the amount of germanium produced for semiconductor electronics is one fiftieth the amount of ultra-high purity silicon produced for the same. Presently, the end uses are fibre-optic systems, infrared optics, solar cell applications. Germanium compounds are used for polymerization catalysts and have most recently found use in the production of nanowires. This element forms a number of organometallic compounds, such as tetraethylgermane. Germanium is not thought to be an element for any living organism. Some complex organic compounds are being investigated as possible pharmaceuticals. Similar to silicon and aluminum, natural germanium compounds tend to be insoluble in water, synthetic soluble germanium salts are nephrotoxic, and synthetic chemically reactive germanium compounds with halogens and hydrogen are irritants and toxins.
Because of its position in his Periodic Table, Mendeleev called it ekasilicon, in mid-1885, at a mine near Freiberg, Saxony, a new mineral was discovered and named argyrodite because of the high silver content. The chemist Clemens Winkler analyzed this new mineral, which proved to be a combination of silver, Winkler was able to isolate the new element in 1886 and found it similar to antimony
Graphite, archaically referred to as plumbago, is a crystalline form of carbon, a semimetal, a native element mineral, and one of the allotropes of carbon. Graphite is the most stable form of carbon under standard conditions, therefore, it is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds. Highly ordered pyrolytic graphite or more correctly highly oriented pyrolytic graphite refers to graphite with a spread between the graphite sheets of less than 1°. The name graphite fiber is sometimes used to refer to carbon fibers or carbon fiber-reinforced polymer. Graphite occurs in rocks as a result of the reduction of sedimentary carbon compounds during metamorphism. It occurs in rocks and in meteorites. Minerals associated with graphite include quartz, calcite and tourmaline, in meteorites it occurs with troilite and silicate minerals. Small graphitic crystals in meteoritic iron are called cliftonite, Graphite is not mined in the United States, but U. S. production of synthetic graphite in 2010 was 134 kt valued at $1.07 billion.
Graphite has a layered, planar structure, the individual layers are called graphene. In each layer, the atoms are arranged in a honeycomb lattice with separation of 0.142 nm. Atoms in the plane are bonded covalently, with three of the four potential bonding sites satisfied. The fourth electron is free to migrate in the plane, making graphite electrically conductive, however, it does not conduct in a direction at right angles to the plane. Bonding between layers is via weak van der Waals bonds, which allows layers of graphite to be easily separated, the two known forms of graphite and beta, have very similar physical properties, except for that the graphene layers stack slightly differently. The alpha graphite may be flat or buckled. The alpha form can be converted to the form through mechanical treatment. The acoustic and thermal properties of graphite are highly anisotropic, since phonons propagate quickly along the tightly-bound planes, graphites high thermal stability and electrical and thermal conductivity facilitate its widespread use as electrodes and refractories in high temperature material processing applications.
However, in oxygen containing atmospheres graphite readily oxidizes to form CO2 at temperatures of 700 °C, Graphite is an electric conductor, useful in such applications as arc lamp electrodes. It can conduct electricity due to the vast electron delocalization within the carbon layers and these valence electrons are free to move, so are able to conduct electricity
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a golden tinge. Nickel belongs to the metals and is hard and ductile. Meteoric nickel is found in combination with iron, a reflection of the origin of elements as major end products of supernova nucleosynthesis. An iron–nickel mixture is thought to compose Earths inner core, use of nickel has been traced as far back as 3500 BCE. Nickel was first isolated and classified as an element in 1751 by Axel Fredrik Cronstedt. The elements name comes from a mischievous sprite of German miner mythology, Nickel, an economically important source of nickel is the iron ore limonite, which often contains 1–2% nickel. Nickels other important ore minerals include garnierite, and pentlandite, major production sites include the Sudbury region in Canada, New Caledonia in the Pacific, and Norilsk in Russia. Nickel is slowly oxidized by air at room temperature and is considered corrosion-resistant, historically, it has been used for plating iron and brass, coating chemistry equipment, and manufacturing certain alloys that retain a high silvery polish, such as German silver.
About 6% of world production is still used for corrosion-resistant pure-nickel plating. Nickel-plated objects sometimes provoke nickel allergy, Nickel has been widely used in coins, though its rising price has led to some replacement with cheaper metals in recent years. Nickel is one of four elements that are ferromagnetic around room temperature, alnico permanent magnets based partly on nickel are of intermediate strength between iron-based permanent magnets and rare-earth magnets. The metal is valuable in modern times chiefly in alloys, about 60% of world production is used in nickel-steels, other common alloys and some new superalloys comprise most of the remainder of world nickel use, with chemical uses for nickel compounds consuming less than 3% of production. As a compound, nickel has a number of chemical manufacturing uses. Nickel is a nutrient for some microorganisms and plants that have enzymes with nickel as an active site. Nickel is a metal with a slight golden tinge that takes a high polish.
It is one of four elements that are magnetic at or near room temperature. Its Curie temperature is 355 °C, meaning that bulk nickel is non-magnetic above this temperature, the unit cell of nickel is a face-centered cube with the lattice parameter of 0.352 nm, giving an atomic radius of 0.124 nm
Schreibersite is generally a rare iron nickel phosphide mineral, 3P, though common in iron-nickel meteorites. The only known occurrence of the mineral on Earth is located on Disko Island in Greenland, another name used for the mineral is rhabdite. It forms tetragonal crystals with perfect 001 cleavage and its color ranges from bronze to brass yellow to silver white. It has a density of 7.5 and a hardness of 6.5 –7 and it is opaque with a metallic luster and a dark gray streak. It was named after the Austrian scientist Carl Franz Anton Ritter von Schreibers, in 2007, researchers reported that schreibersite and other meteoric phosphorus bearing minerals may be the ultimate source for the phosphorus that is so important for life on Earth. They hypothesized that their experiment might represent what they termed chemical life, glossary of meteoritics List of minerals List of minerals named after people
The Iron Age is an archaeological era, referring to a period of time in the prehistory and protohistory of the Old World when the dominant toolmaking material was iron. It is commonly preceded by the Bronze Age in Europe and Asia with exceptions, meteoric iron has been used by humans since at least 3200 BC. Ancient iron production did not become widespread until the ability to smelt ore, remove impurities. The start of the Iron Age proper is considered by many to fall between around 1200 BC and 600 BC, depending on the region, the earliest known iron artifacts are nine small beads dated to 3200 BC, which were found in burials at Gerzeh, Lower Egypt. They have been identified as meteoric iron shaped by careful hammering, meteoric iron, a characteristic iron–nickel alloy, was used by various ancient peoples thousands of years before the Iron Age. Such iron, being in its metallic state, required no smelting of ores. Smelted iron appears sporadically in the record from the middle Bronze Age. While terrestrial iron is abundant, its high melting point of 1,538 °C placed it out of reach of common use until the end of the second millennium BC.
Tins low melting point of 231, recent archaeological remains of iron working in the Ganges Valley in India have been tentatively dated to 1800 BC. By the Middle Bronze Age, increasing numbers of smelted iron objects appeared in the Middle East, Southeast Asia, African sites are turning up dates as early as 1200 BC. Modern archaeological evidence identifies the start of iron production in around 1200 BC. Between 1200 BC and 1000 BC, diffusion in the understanding of iron metallurgy and use of objects was fast. As evidence, many bronze implements were recycled into weapons during this time, more widespread use of iron led to improved steel-making technology at lower cost. Thus, even when tin became available again, iron was cheaper and lighter, and forged iron implements superseded cast bronze tools permanently. Increasingly, the Iron Age in Europe is being seen as a part of the Bronze Age collapse in the ancient Near East, in ancient India, ancient Iran, and ancient Greece. In other regions of Europe, the Iron Age began in the 8th century BC in Central Europe, the Near Eastern Iron Age is divided into two subsections, Iron I and Iron II.
Iron I illustrates both continuity and discontinuity with the previous Late Bronze Age, during the Iron Age, the best tools and weapons were made from steel, particularly alloys which were produced with a carbon content between approximately 0. 30% and 1. 2% by weight. Steel weapons and tools were nearly the same weight as those of bronze, steel was difficult to produce with the methods available, and alloys that were easier to make, such as wrought iron, were more common in lower-priced goods