The kilogram or kilogramme is the base unit of mass in the International System of Units. Until 20 May 2019, it remains defined by a platinum alloy cylinder, the International Prototype Kilogram, manufactured in 1889, stored in Saint-Cloud, a suburb of Paris. After 20 May, it will be defined in terms of fundamental physical constants; the kilogram was defined as the mass of a litre of water. That was an inconvenient quantity to replicate, so in 1799 a platinum artefact was fashioned to define the kilogram; that artefact, the IPK, have been the standard of the unit of mass for the metric system since. In spite of best efforts to maintain it, the IPK has diverged from its replicas by 50 micrograms since their manufacture late in the 19th century; this led to efforts to develop measurement technology precise enough to allow replacing the kilogram artifact with a definition based directly on physical phenomena, now scheduled to take place in 2019. The new definition is based on invariant constants of nature, in particular the Planck constant, which will change to being defined rather than measured, thereby fixing the value of the kilogram in terms of the second and the metre, eliminating the need for the IPK.
The new definition was approved by the General Conference on Weights and Measures on 16 November 2018. The Planck constant relates a light particle's energy, hence mass, to its frequency; the new definition only became possible when instruments were devised to measure the Planck constant with sufficient accuracy based on the IPK definition of the kilogram. The gram, 1/1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimetre of water at the melting point of ice; the final kilogram, manufactured as a prototype in 1799 and from which the International Prototype Kilogram was derived in 1875, had a mass equal to the mass of 1 dm3 of water under atmospheric pressure and at the temperature of its maximum density, 4 °C. The kilogram is the only named SI unit with an SI prefix as part of its name; until the 2019 redefinition of SI base units, it was the last SI unit, still directly defined by an artefact rather than a fundamental physical property that could be independently reproduced in different laboratories.
Three other base units and 17 derived units in the SI system are defined in relation to the kilogram, thus its stability is important. The definitions of only eight other named SI units do not depend on the kilogram: those of temperature and frequency, angle; the IPK is used or handled. Copies of the IPK kept by national metrology laboratories around the world were compared with the IPK in 1889, 1948, 1989 to provide traceability of measurements of mass anywhere in the world back to the IPK; the International Prototype Kilogram was commissioned by the General Conference on Weights and Measures under the authority of the Metre Convention, in the custody of the International Bureau of Weights and Measures who hold it on behalf of the CGPM. After the International Prototype Kilogram had been found to vary in mass over time relative to its reproductions, the International Committee for Weights and Measures recommended in 2005 that the kilogram be redefined in terms of a fundamental constant of nature.
At its 2011 meeting, the CGPM agreed in principle that the kilogram should be redefined in terms of the Planck constant, h. The decision was deferred until 2014. CIPM has proposed revised definitions of the SI base units, for consideration at the 26th CGPM; the formal vote, which took place on 16 November 2018, approved the change, with the new definitions coming into force on 20 May 2019. The accepted redefinition defines the Planck constant as 6.62607015×10−34 kg⋅m2⋅s−1, thereby defining the kilogram in terms of the second and the metre. Since the second and metre are defined in terms of physical constants, the kilogram is defined in terms of physical constants only; the avoirdupois pound, used in both the imperial and US customary systems, is now defined in terms of the kilogram. Other traditional units of weight and mass around the world are now defined in terms of the kilogram, making the kilogram the primary standard for all units of mass on Earth; the word kilogramme or kilogram is derived from the French kilogramme, which itself was a learned coinage, prefixing the Greek stem of χίλιοι khilioi "a thousand" to gramma, a Late Latin term for "a small weight", itself from Greek γράμμα.
The word kilogramme was written into French law in 1795, in the Decree of 18 Germinal, which revised the older system of units introduced by the French National Convention in 1793, where the gravet had been defined as weight of a cubic centimetre of water, equal to 1/1000 of a grave. In the decree of 1795, the term gramme thus replaced gravet, kilogramme replaced grave; the French spelling was adopted in Great Britain when the word was used for the first time in English in 1795, with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with "kilogram" having become by far the more common. UK law regulating the units to be used when trading by weight or measure does not prevent the use of either spelling. In the 19th century the French word kilo, a shortening of kilogramme, was imported into the English language where it has been used to mean both kilogram and kilometre. While kilo is acceptable in many generalist texts
A meteorite hunting is the search for meteorites. A person engaged in the search for meteorites is known as a meteorite hunter. Meteorite hunters may be amateurs who search on the weekends and after work, or professionals who recover meteorites for a living. Both use tools such as metal detectors or magnets to discover the meteorites. If the meteorite is of the iron or stony iron variety a magnet will pick it up from the soil surface or a metal detector will detect it through many inches of soil. Stony meteorites —which make up the large majority of meteorites that fall— may not have a high enough nickel iron content to set off a metal detector. Large and sensitive metal detectors may be used as well as ground-penetrating radar and landmine detectors. Although meteorites fall uniformly across the globe they do not remain on the surface in areas with a large amount of yearly rainfall. If a newly fallen meteorite is not recovered within a few months it is to be buried with alluvium or covered by plant growth.
Some arctic and desert regions have proven to be well-suited to preserving meteorites, can provide excellent surfaces for hunting visually. Meteorites can be valuable to scientists studying planetary science and to collectors. Individual stones may weigh mere hundreds of kilograms, their values vary based on rarity and composition, as well as the conditions in which they are found. In the United States, most state laws state that a meteorite find belongs to the landowner of the land upon which the meteorite was found; this doctrine contrasts with the once-predominant rule in state courts on the finding of treasure trove, where buried gold or silver coinage is deemed to belong to the finder. Many state courts have interpreted their laws as granting the state sole title to any meteorite recovered on state-owned lands. United States laws and enforcement of laws regarding recovery of meteorites on federally owned public lands is unsettled. With respect to large meteorites, the federal government has asserted title to all such meteorites if proven to be found on federal land, because: the meteorite is the property of the federal government, the landowner meteorites found on public lands are subject to the 1906 Antiquities Act a meteorite does not qualify as a “valuable mineral” as defined under the 1872 Mining Law, thus it is not subject to mineral claim rights that could otherwise be filed by the discoverer.
This policy derives from cases as far back as 1944, when the federal government seized the Drum Mountain Meteorite in Utah from a group of interned Japanese-American U. S. citizens. The federal government has sometimes agreed to negotiate sometimes negotiating a small finders fee for large meteorites, but has never agreed to pay anything resembling full market value of the meteorite to the discoverer. In the case of small meteorites, ownership of meteorites found on federal land is not covered in the Code of Federal Regulations, in the past hobbyists have been able to remove small quantities of rock for non-commercial use. However, in recent years the U. S. Bureau of Land Management has asserted that it owns all meteorites recovered on BLM land arguing that BLM stands in the same position as a private landowner under state law; the BLM further asserts that under the 1906 Antiquities Act, all meteorites on BLM land belong to the Smithsonian Institution. A BLM memorandum of September 10, 2012, reaffirms that meteorites found on public land belong to the Federal Government.
Permits can be acquired for systematic search for meteorites on public land undertaken for scientific, educational, or commercial purposes. Antarctic prospecting is expensive and therefore can only be carried on by well funded organizations. Half of the meteorites found in Antarctica have been recovered by ANSMET; the ANSMET program is a major source of the extraterrestrial material, available for scientific investigation. Japanese finds make up the majority of the remainder, China has begun exploration. A popular geological feature employed by Antarctic meteorite hunters is an area where a natural downsloped plain meets an uprising ridge, such as where the East Antarctic Ice Sheet, creeping to the sea at about three metres per year, meets the Transantarctic Mountains; the downslope-mountain ridge combination allows the creeping gravity-driven icesheet to start rising upwards. As it does so, the exposed snow and ice are removed by fierce winds and sublimation harvesting the embedded meteorites and leaving them to lie on the surface along the length of the mountain ridge.
The famed 1.93 kilograms Allan Hills 84001 meteorite abbreviated as ALH 84001 and believed to be from Mars, was found at Allan Hills, Antarctica in 1984. In 1996 NASA scientists announced that it might contain evidence for microscopic fossils of Martian bacteria based on the carbonate globules it contained. In the aftermath of the air burst of a meteor, a large number of small meteorites can fall to the ground at terminal velocity, such as occurred with the 2013 Chelyabinsk meteor; when that occurs local residents and schoolchildren will seek to locate and pick up the fragments due to their potential value. In the case of the Chelyabinsk meteor, many were located in snowdrifts by following a visible hole, left in the outer surface of the snow. Meteorite Men is a U. S. television series following two atypical meteorite hunters. Glossary of meteoritics
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. Thus it is a type of orthosilicate, it is a common mineral in Earth's subsurface but weathers on the surface. The ratio of magnesium to iron varies between the two endmembers of the solid solution series: forsterite and fayalite. Compositions of olivine are expressed as molar percentages of forsterite and fayalite. Forsterite's melting temperature is unusually high at atmospheric pressure 1,900 °C, while fayalite's is much lower. Melting temperature varies smoothly between the two endmembers. Olivine incorporates only minor amounts of elements other than oxygen, silicon and iron. Manganese and nickel are the additional elements present in highest concentrations. Olivine gives its name to the group of minerals with a related structure —which includes tephroite and kirschsteinite. Olivine's crystal structure incorporates aspects of the orthorhombic P Bravais lattice, which arise from each silica unit being joined by metal divalent cations with each oxygen in SiO4 bound to 3 metal ions.
It has a spinel-like structure similar to magnetite but uses one quadrivalent and two divalent cations M22+ M4+O4 instead of two trivalent and one divalent cations. Olivine gemstones are called chrysolite. Olivine rock is harder than surrounding rock and stands out as distinct ridges in the terrain; these ridges are dry with little soil. Drought resistant scots pine is one of few trees. Olivine pine forest is unique to Norway, it found on dry olivine ridges in the fjord districts of Sunnmøre and Nordfjord. Olivine rock is base-rich; the habitat is endangered by road construction. Olivine is named for its olive-green color, though it may alter to a reddish color from the oxidation of iron. Translucent olivine is sometimes used as a gemstone called peridot, it is called chrysolite. Some of the finest gem-quality olivine has been obtained from a body of mantle rocks on Zabargad Island in the Red Sea. Olivine occurs in both mafic and ultramafic igneous rocks and as a primary mineral in certain metamorphic rocks.
Mg-rich olivine crystallizes from magma, rich in magnesium and low in silica. That magma crystallizes to mafic rocks such as basalt. Ultramafic rocks such as peridotite and dunite can be residues left after extraction of magmas, they are more enriched in olivine after extraction of partial melts. Olivine and high pressure structural variants constitute over 50% of the Earth's upper mantle, olivine is one of the Earth's most common minerals by volume; the metamorphism of impure dolomite or other sedimentary rocks with high magnesium and low silica content produces Mg-rich olivine, or forsterite. Fe-rich olivine is much less common, but it occurs in igneous rocks in small amounts in rare granites and rhyolites, Fe-rich olivine can exist stably with quartz and tridymite. In contrast, Mg-rich olivine does not occur stably with silica minerals, as it would react with them to form orthopyroxene. Mg-rich olivine is stable to pressures equivalent to a depth of about 410 km within Earth; because it is thought to be the most abundant mineral in Earth’s mantle at shallower depths, the properties of olivine have a dominant influence upon the rheology of that part of Earth and hence upon the solid flow that drives plate tectonics.
Experiments have documented that olivine at high pressures can contain at least as much as about 8900 parts per million of water, that such water content drastically reduces the resistance of olivine to solid flow. Moreover, because olivine is so abundant, more water may be dissolved in olivine of the mantle than is contained in Earth's oceans. Mg-rich olivine has been discovered in meteorites, on the Moon and Mars, falling into infant stars, as well as on asteroid 25143 Itokawa; such meteorites include collections of debris from the early Solar System. The spectral signature of olivine has been seen in the dust disks around young stars; the tails of comets have the spectral signature of olivine, the presence of olivine was verified in samples of a comet from the Stardust spacecraft in 2006. Comet-like olivine has been detected in the planetesimal belt around the star Beta Pictoris. Minerals in the olivine group crystallize in the orthorhombic system with isolated silicate tetrahedra, meaning that olivine is a nesosilicate.
In an alternative view, the atomic structure can be described as a hexagonal, close-packed array of oxygen ions with half of the octahedral sites occupied with magnesium or iron ions and one-eighth of the tetrahedral sites occupied by silicon ions. There are two distinct metal sites and only one distinct silicon site. O1, O2, M2 and Si all lie on mirror planes. O3 lies in a general position. At the high temperatures and pressures found at depth within the Earth the olivine structure is no longer stable. Below depths of about 410 km olivine undergoes an exothermic phase transition to the sorosilicate, wadsleyite and, at a
The L type ordinary chondrites are the second most common group of meteorites, accounting for 35% of all those catalogued, 40% of the ordinary chondrites. The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively, their name comes from their low iron abundance, with respect to the H chondrites, which are about 20–25% iron by weight. The L chondrites have been named hypersthene chondrites or olivine hypersthene chondrites for the dominant minerals, but these terms are now obsolete. Characteristic is the fayalite content in olivine of 21 to 25 mol%. About 4–10% iron–nickel is found as a free metal, making these meteorites magnetic, but not as as the H chondrites; the most abundant minerals are hypersthene, as well as iron -- nickel and troilite. Chromite, sodium-rich feldspar and calcium phosphates occur in minor amounts. Petrologic type 6 dominates, with over 60% of the L chondrites falling into this class.
This indicates. Many of the L chondrite meteors may have their origin in the Ordovician meteor event. Compared to other chondrites, a large proportion of the L chondrites have been shocked, taken to imply that the parent body was catastrophically disrupted by a large impact; this event has been radioisotope dated to around 470±6 million years ago. The parent body/bodies for this group are not known, but plausible suggestions include 433 Eros and 8 Flora, or the Flora family as a whole. 433 Eros has been found to have a similar spectrum, while several pieces of circumstantial evidence for the Flora family exist: the Flora family is thought to have formed about 1,000 to 500 million years ago. Glossary of meteoritics The Catalogue of Meteorites
Germanium is a chemical element with symbol Ge and atomic number 32. It is a lustrous, grayish-white metalloid in the carbon group, chemically similar to its group neighbours silicon and tin. Pure germanium is a semiconductor with an appearance similar to elemental silicon. Like silicon, germanium reacts and forms complexes with oxygen in nature; because it appears in high concentration, germanium was discovered comparatively late in the history of chemistry. Germanium ranks near fiftieth in relative abundance of the elements in the Earth's crust. In 1869, Dmitri Mendeleev predicted its existence and some of its properties from its position on his periodic table, called the element ekasilicon. Nearly two decades in 1886, Clemens Winkler found the new element along with silver and sulfur, in a rare mineral called argyrodite. Although the new element somewhat resembled arsenic and antimony in appearance, the combining ratios in compounds agreed with Mendeleev's predictions for a relative of silicon.
Winkler named the element after Germany. Today, germanium is mined from sphalerite, though germanium is recovered commercially from silver and copper ores. Elemental germanium is used as a semiconductor in various other electronic devices; the first decade of semiconductor electronics was based on germanium. Presently, the major end uses are fibre-optic systems, infrared optics, solar cell applications, light-emitting diodes. Germanium compounds are used for polymerization catalysts and have most found use in the production of nanowires; this element forms a large number of organogermanium compounds, such as tetraethylgermanium, useful in organometallic chemistry. Germanium is considered a technology-critical element. Germanium is not thought to be an essential element for any living organism; some complex organic germanium compounds are being investigated as possible pharmaceuticals, though none have yet proven successful. Similar to silicon and aluminium, natural germanium compounds tend to be insoluble in water and thus have little oral toxicity.
However, synthetic soluble germanium salts are nephrotoxic, synthetic chemically reactive germanium compounds with halogens and hydrogen are irritants and toxins. In his report on The Periodic Law of the Chemical Elements in 1869, the Russian chemist Dmitri Mendeleev predicted the existence of several unknown chemical elements, including one that would fill a gap in the carbon family, located between silicon and tin; because of its position in his periodic table, Mendeleev called it ekasilicon, he estimated its atomic weight to be 70. In mid-1885, at a mine near Freiberg, Saxony, a new mineral was discovered and named argyrodite because of its high silver content; the chemist Clemens Winkler analyzed this new mineral, which proved to be a combination of silver, a new element. Winkler found it similar to antimony, he considered the new element to be eka-antimony, but was soon convinced that it was instead eka-silicon. Before Winkler published his results on the new element, he decided that he would name his element neptunium, since the recent discovery of planet Neptune in 1846 had been preceded by mathematical predictions of its existence.
However, the name "neptunium" had been given to another proposed chemical element. So instead, Winkler named the new element germanium in honor of his homeland. Argyrodite proved empirically to be Ag8GeS6; because this new element showed some similarities with the elements arsenic and antimony, its proper place in the periodic table was under consideration, but its similarities with Dmitri Mendeleev's predicted element "ekasilicon" confirmed that place on the periodic table. With further material from 500 kg of ore from the mines in Saxony, Winkler confirmed the chemical properties of the new element in 1887, he determined an atomic weight of 72.32 by analyzing pure germanium tetrachloride, while Lecoq de Boisbaudran deduced 72.3 by a comparison of the lines in the spark spectrum of the element. Winkler was able to prepare several new compounds of germanium, including fluorides, sulfides and tetraethylgermane, the first organogermane; the physical data from those compounds—which corresponded well with Mendeleev's predictions—made the discovery an important confirmation of Mendeleev's idea of element periodicity.
Here is a comparison between the prediction and Winkler's data: Until the late 1930s, germanium was thought to be a poorly conducting metal. Germanium did not become economically significant until after 1945 when its properties as an electronic semiconductor were recognized. During World War II, small amounts of germanium were used in some special electronic devices diodes; the first major use was the point-contact Schottky diodes for radar pulse detection during the War. The first silicon-germanium alloys were obtained in 1955. Before 1945, only a few hundred kilograms of germanium were produced in smelters each year, but by the end of the 1950s, the annual worldwide production had reached 40 metric tons; the development of the germanium transistor in 1948 opened the door to countless applications of solid state electronics. From 1950 through the early 1970s, this area provided an increasing market for germanium, but high-purity silicon began replacing germanium in transistors and rectifiers.
For example, the company that became Fairchild Semiconductor was founded in 1957 with the express purpose of producing silicon transist
An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystallization on or within meteorite parent bodies; as a result, achondrites have distinct mineralogies indicative of igneous processes. Achondrites account for about 8% of meteorites overall, the majority of them are HED meteorites originating from the crust of asteroid 4 Vesta. Other types include Martian and several types thought to originate from as-yet unidentified asteroids; these groups have been determined on the basis of e.g. the Fe/Mn chemical ratio and the 17O/18O oxygen isotope ratios, thought to be characteristic "fingerprints" for each parent body. Achondrites are classified into the following groups: Primitive achondrites Asteroidal achondrites Lunar meteorites Martian meteorites Primitive achondrites called PAC group, are called in this way because their chemical composition is primitive in the sense that it is similar to the composition of chondrites, but their texture is igneous, indicative of melting processes.
To this group belong: Acapulcoites Lodranites Winonaites Ureilites Brachinites Asteroidal achondrites called evolved achondrites, are called in this way because have been differentiated on a parent body. This means that their mineralogical and chemical composition was changed by melting and crystallization processes, they are divided several groups: HED meteorites. They may have originated on the asteroid 4 Vesta, because their reflection spectra are similar, they are named after the initial letters of the three subgroups: Howardites Eucrites Diogenites Angrites Aubrites Lunar meteorites are meteorites that originated from the Moon. Martian meteorites are meteorites, they are divided into three main groups, with two exceptions: Shergottites Nakhlites Chassignites OPX martian meteorites Regolith/Soil samples Glossary of meteoritics Achondrite Images from Meteorites Australia
The LL chondrites are a group of stony meteorites, the least abundant group of the ordinary chondrites, accounting for about 10–11% of observed ordinary-chondrite falls and 8–9% of all meteorite falls. The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively; the composition of the Chelyabinsk meteor is that of a LL chondrite meteorite. The material makeup of Itokawa, the asteroid visited by the Hayabusa spacecraft which landed on it and brought particles back to Earth proved to be type LL chondrite. LL stands for Low metal, they contain only 0.3 -- 3 % metallic iron. That means; the most abundant minerals are olivine. Other minerals include Fe–Ni, feldspar or feldspathic glass and phosphates. LL chondrites contain the largest chondrules of the ordinary chondrite groups, averaging around 1 millimetre diameter; the LL group includes many of the most primitive ordinary chondrites, including the well-studied Semarkona chondrite.
However, most LL chondrites have been thermally metamorphosed to petrologic types 5 and 6, meaning that their minerals are homogeneous in composition and chondrule borders are difficult to discern. This, together with the low content of metal, led the 19th century mineralogist Tschermak to determine that they formed a transitional stage between chondrites and achondrites and to name them amphoterites. We know now that LL chondrites and achondrites are quite different, so this name is no longer in use. Many of the LL chondrites are breccias. Glossary of meteoritics S-type asteroid F. Heide and F. Wlotzka, Meteorites: Messengers from Space. Springer-Verlag, 1995