Schreger lines are the unique identifiers of what valuable substance whose usage has led to the dwindling numbers of something large?
"Schreger line Schreger lines are visual artifacts that are evident in the cross-sections of ivory. They are commonly referred to as cross-hatchings, engine turnings, or stacked chevrons. Schreger lines can be divided into two categories. The easily seen lines which are closest to the cementum are the ""outer Schreger lines"". The faintly discernible lines found around the tusk nerve or pulp cavities are the ""inner Schreger lines"". The intersections of Schreger lines form angles, which appear in two forms: concave angles and convex angles. Concave angles have slightly concave sides and open to the medial (inner) area of the tusk."
"Paneth (1887-1958). Panethite Panethite (Na,Ca)(Mg,Fe)(PO) is a rare phosphate mineral that was only found in one meteorite on Earth. It was originally found in the Dayton meteorite in Ohio. It is classified as H-M symbol (2/m) with space group of ""P""2/n. It is amber in color. It was named in the honor of Friedrich Adolf Paneth (1887–1958), a German chemist who made many contributions toward the discovery of the origin of the universe, and especially studies of meteorites. Using X-ray diffraction, the unit cell and the space group parameters were determined. The strongest lines of the X-ray were 5.10(6), 3.236(5),"
"insoluble impurities in natural platinum. Smithson Tennant, the primary discoverer, named the iridium for the goddess Iris, personification of the rainbow, because of the striking and diverse colors of its salts. Iridium is one of the rarest elements in the Earth's crust, with annual production and consumption of only three tonnes. and are the only two naturally occurring isotopes of iridium as well as the only stable isotopes; the latter is the more abundant of the two. The most important iridium compounds in use are the salts and acids it forms with chlorine, though iridium also forms a number of"
"America, 30–50% of current fiber optic lines are unused dark fiber, sparking discussion of over-production and a future reduction in demand. Worldwide, demand is increasing dramatically as countries such as China are installing fiber optic telecommunication lines throughout the country. Germanium Germanium is a chemical element with symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. Pure germanium is a semiconductor with an appearance similar to elemental silicon. Like silicon, germanium naturally reacts and forms complexes with oxygen in nature. Because it seldom"
"Panethite Panethite (Na,Ca)(Mg,Fe)(PO) is a rare phosphate mineral that was only found in one meteorite on Earth. It was originally found in the Dayton meteorite in Ohio. It is classified as H-M symbol (2/m) with space group of ""P""2/n. It is amber in color. It was named in the honor of Friedrich Adolf Paneth (1887–1958), a German chemist who made many contributions toward the discovery of the origin of the universe, and especially studies of meteorites. Using X-ray diffraction, the unit cell and the space group parameters were determined. The strongest lines of the X-ray were 5.10(6), 3.236(5), 3.007(10), 2.749,"
"electrical contacts and the production of thick-film resistors. A minor application of ruthenium is its use in some platinum alloys. Rhodium is a chemical element that is a rare, silvery-white, hard, and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. It is composed of only one isotope,Rh. Naturally occurring rhodium is found as the free metal, alloyed with similar metals, and never as a chemical compound. It is one of the rarest precious metals and one of the most costly (gold has since taken over the top"
"metal-free, it does not belong to the first generation of stars (the hypothetical Population III). These stars converted the pristine hydrogen, helium, and lithium formed by the Big Bang into heavier elements, such as carbon, oxygen, and metals. The star is relatively small for a star of the early universe, which accounts for its old age: massive stars die quickly. To help explain why this star is so small, it is hypothesized it was once part of a binary star system. HE0107-5240 was found by Norbert Christlieb and colleagues at the University of Hamburg in Germany as a byproduct of"
"such as mercury, thallium, and arsenic are toxic and so are difficult to find or their sale is restricted. Others are extremely rare in commercial use, such as scandium, lutetium and thulium and are therefore hard to source or are comparatively expensive. Some, such as caesium and fluorine, are too reactive and have restrictions on their shipping; others, such as gallium, react corrosively and very fast with aluminium (e.g., as structural material in aircraft). Others, like radon and astatine are radioactive and have half-lifes too short for practical collection in addition to their radioactive hazards. Usually only the stable elements"
"data was also available for some developing nations). Extant in-use metal-stock estimations for the major engineering metals: Some primary stocks of rare but useful metals are already running low. For example, rhenium only occurs at seven parts per billion in the Earth’s crust, making it one of the rarest elements on the planet. However, its high melting point of 3,186 °C makes it valuable in the manufacture of jet engines. Demand for the metal is rising, with increasing air travel, but its rarity means increasing extraction is not simple. This is where recycling comes in; rhenium is one of the"
"only mercury, lead and bismuth meet all of them. Despite this lack of agreement, the term (plural or singular) is widely used in science. A density of more than 5 g/cm is sometimes quoted as a commonly used criterion and is used in the body of this article. The earliest known metals—common metals such as iron, copper, and tin, and precious metals such as silver, gold, and platinum—are heavy metals. From 1809 onwards, light metals, such as magnesium, aluminium, and titanium, were discovered, as well as less well-known heavy metals including gallium, thallium, and hafnium. Some heavy metals are either"
"and health. Tellurium Tellurium is a chemical element with symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur. It is occasionally found in native form as elemental crystals. Tellurium is far more common in the universe as a whole than on Earth. Its extreme rarity in the Earth's crust, comparable to that of platinum, is due partly to its high atomic number, but also to its formation of a volatile hydride which caused it to be lost to space as a gas during the hot nebular"
"shows in its compounds a wide variety of oxidation states ranging from −1 to +7. Discovered in 1925, rhenium was the last stable element to be discovered. It was named after the river Rhine in Europe. Nickel-based superalloys of rhenium are used in the combustion chambers, turbine blades, and exhaust nozzles of jet engines, these alloys contain up to 6% rhenium, making jet engine construction the largest single use for the element, with the chemical industry's catalytic uses being next-most important. Because of the low availability relative to demand, rhenium is among the most expensive of metals, with an average"
"years old, helped bolster the theory that stars can produce heavier elements. Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element in 1844 and named it after Ruthenia, the Latin word for Rus'. Ruthenium usually occurs as a minor component of platinum ores and its annual production is only about 12 tonnes worldwide. Most ruthenium is used for wear-resistant"
"shortly after a portion of the area was destroyed to make way for power lines, making the species' continued existence unlikely. About 720 skins and 16 skeletons are housed in museums around the world and analyzable DNA has been extracted from them. The evidence is indicative that humans had at least a contributory role in the extinction of the Carolina parakeet, through a variety of means. Chief was deforestation in the 18th and 19th centuries. Hunting played a significant role, both for decorative use of their colorful feathers, for example, adornment of women's hats, and for reduction of crop predation."
"high-pressure, high-temperature materials more commonly assumed to be exclusive to meteoritic sources, products of asteroid impacts, comet airbursts, or cosmic dust. Such materials - as a suite - formerly considered to be unique to hypervelocity impacts, have been identified in fulgurites, including highly reduced silicon-metal alloys (silicides), the fullerene allotropes C (buckminsterfullerene) and C, as well as high-pressure polymorphs of SiO, collectively known as shocked quartz, in fulgurites. Reduced phosphorus as phosphides and phosphites has been identified through quantitative analyses of a representative sample of 10 fulgurites recovered from most continents, in the form of schreibersite (FeP, (Fe,Ni)P) - otherwise"
"be increasing as computers and mobile phones became more popular in the mid to late 2000s. Thulium is used in x-ray tubes and neodymium is used in high strength/high grade magnets. Molybdenum, rhodium, neodymium and palladium are relatively scarce metals, while manganese and vanadium are, like phosphorus and sulfur, fairly abundant for minor minerals. The major metals such as iron, lead and tin are commonplace. Recycling of the aluminum, ferrous metals, copper fractions, gold, palladium and platinum in mobile phones and computers had got under way by the mid-2000s. Battery recycling has helped bring down both the nickel and cadmium"
"Iridium was discovered in 1803 among insoluble impurities in natural platinum. Smithson Tennant, the primary discoverer, named iridium for the Greek goddess Iris, personification of the rainbow, because of the striking and diverse colors of its salts. Iridium is one of the rarest elements in Earth's crust, with annual production and consumption of only three tonnes. Ir and Ir are the only two naturally occurring isotopes of iridium, as well as the only stable isotopes; the latter is the more abundant of the two. The most important iridium compounds in use are the salts and acids it forms with chlorine,"
"deposited later by meteorites which contained the element. This supposedly explains why, in prehistory, gold appeared as nuggets on the earth's surface. Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum ( < Greek """" ""water"" and """" ""silver""). A heavy, silvery d-block element, mercury is the only metal that is liquid at standard conditions for temperature and pressure; the only other element that is liquid under these conditions is bromine, though metals such as caesium, francium, gallium, and rubidium melt just above room temperature. With a freezing"
"had been authigenically-synthesized during its electro-pyrometamorphic formation. The long-term survivability of chiral organic compounds native to organisms has been demonstrated reliably in carbonaceous chondrites such as the Murchison, a CM chondrite. Reduced phosphorus as phosphides and phosphites have been identified through quantitative analyses of a representative sample of 10 fulgurites recovered from most continents, in the form of schreibersite (FeP, (Fe,Ni)P) - terrestrially extremely rare, but common on meteorites, comets, interplanetary dust, and some planetary bodies - and TiP, which is unique to fulgurites. Reduced phosphorus species were necessary for the development of DNA and RNA in proto-biotic systems that"
"Scandium Scandium is a chemical element with symbol Sc and atomic number 21. A silvery-white metallic d-block element, it has historically been classified as a rare-earth element, together with yttrium and the lanthanides. It was discovered in 1879 by spectral analysis of the minerals euxenite and gadolinite from Scandinavia. Scandium is present in most of the deposits of rare-earth and uranium compounds, but it is extracted from these ores in only a few mines worldwide. Because of the low availability and the difficulties in the preparation of metallic scandium, which was first done in 1937, applications for scandium were not"
"a large meteorite impact; this is the Cretaceous–Paleogene extinction event (also known as the K–T or K–Pg extinction event), which occurred 66 million years ago. There is no definitive evidence of impacts leading to the three other major mass extinctions. In 1980, physicist Luis Alvarez; his son, geologist Walter Alvarez; and nuclear chemists Frank Asaro and Helen V. Michael from the University of California, Berkeley discovered unusually high concentrations of iridium in a specific layer of rock strata in the Earth's crust. Iridium is an element that is rare on Earth but relatively abundant in many meteorites. From the amount"
"Yttrium Yttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a ""rare-earth element"". Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals, and is never found in nature as a free element. Y is the only stable isotope, and the only isotope found in the Earth's crust. In 1787, Carl Axel Arrhenius found a new mineral near Ytterby in Sweden and named it ""ytterbite"", after the village. Johan Gadolin discovered yttrium's oxide in Arrhenius' sample in"
"T. Seaborg. They isolated the metastable isotope technetium-99m, which is now used in some ten million medical diagnostic procedures annually. In 1952, astronomer Paul W. Merrill in California detected the spectral signature of technetium (specifically wavelengths of 403.1 nm, 423.8 nm, 426.2 nm, and 429.7 nm) in light from S-type red giants. The stars were near the end of their lives, yet were rich in this short-lived element, indicating that it was being produced in the stars by nuclear reactions. This evidence bolstered the hypothesis that heavier elements are the product of nucleosynthesis in stars. More recently, such observations provided"
"between the impact and global longer-term effects on the climate and food chain. In 1980, a team of researchers led by Nobel prize-winning physicist Luis Alvarez, his son, geologist Walter Alvarez, and chemists Frank Asaro and Helen Vaughn Michel discovered that sedimentary layers found all over the world at the Cretaceous–Paleogene boundary (K–Pg boundary, formerly called Cretaceous–Tertiary or K–T boundary) contain a concentration of iridium hundreds of times greater than normal. Iridium is extremely rare in the Earth's crust because it is very dense and has the affinity for iron that characterizes the siderophile elements (see Goldschmidt classification), and therefore"
"line is called ""Lyman-alpha"" (Ly-α), while the line is called ""Paschen-delta” (Pa-δ). There are emission lines from hydrogen that fall outside of these series, such as the 21 cm line. These emission lines correspond to much rarer atomic events such as hyperfine transitions. The fine structure also results in single spectral lines appearing as two or more closely grouped thinner lines, due to relativistic corrections. In quantum mechanical theory, the discrete spectrum of atomic emission was based on the Schrödinger equation, which is mainly devoted to the study of energy spectra of hydrogenlike atoms, whereas the time-dependent equivalent Heisenberg equation"
"Tellurium Tellurium is a chemical element with symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur. It is occasionally found in native form as elemental crystals. Tellurium is far more common in the universe as a whole than on Earth. Its extreme rarity in the Earth's crust, comparable to that of platinum, is due partly to its high atomic number, but also to its formation of a volatile hydride which caused it to be lost to space as a gas during the hot nebular formation of"
"one decay per second), and the inhalation limit at 6000 Bq. Mendelevium Mendelevium is a synthetic element with chemical symbol Md (formerly Mv) and atomic number 101. A metallic radioactive transuranic element in the actinide series, it is the first element that currently cannot be produced in macroscopic quantities through neutron bombardment of lighter elements. It is the third-to-last actinide and the ninth transuranic element. It can only be produced in particle accelerators by bombarding lighter elements with charged particles. A total of sixteen mendelevium isotopes are known, the most stable being Md with a half-life of 51 days; nevertheless,"
"oxide and siliceous beryllium (ASTM D7458). Beryllium Beryllium is a chemical element with symbol Be and atomic number 4. It is a relatively rare element in the universe, usually occurring as a product of the spallation of larger atomic nuclei that have collided with cosmic rays. Within the cores of stars beryllium is depleted as it is fused and creates larger elements. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl (aquamarine, emerald) and chrysoberyl. As a free element it is a steel-gray, strong, lightweight and"
"are potassium, uranium and thorium and their decay products, some of which, like radium and radon are intensely radioactive but occur in low concentrations. Most of these sources have been decreasing, due to radioactive decay since the formation of the Earth, because there is no significant amount currently transported to the Earth. Thus, the present activity on earth from uranium-238 is only half as much as it originally was because of its 4.5 billion year half-life, and potassium-40 (half-life 1.25 billion years) is only at about 8% of original activity. But during the time that humans have existed the amount"
"ranging from −1 to +7. Discovered in 1908, rhenium was the second-last stable element to be discovered. It was named after the river Rhine in Europe. Nickel-based superalloys of rhenium are used in the combustion chambers, turbine blades, and exhaust nozzles of jet engines. These alloys contain up to 6% rhenium, making jet engine construction the largest single use for the element. The second-most important use is as a catalyst: rhenium is an excellent catalyst for hydrogenation and isomerization, and is used for example in catalytic reforming of naphtha for use in gasoline (Rheniforming process). Because of the low availability"
"rare. It was once used for its semiconductor properties pretty much as silicon is now, and it has some superior properties at that, but is now a rare material in the industry. Arsenic is a toxic metalloid that has been used throughout history as an additive to metal alloys, paints, and even makeup. Antimony is used as a constituent in casting alloys such as printing metal. Previously called inert gases, their name was changed as there are a few other gases that are inert but not noble gases, such as nitrogen. The noble gases are located in the far right"
"Beryllium Beryllium is a chemical element with symbol Be and atomic number 4. It is a relatively rare element in the universe, usually occurring as a product of the spallation of larger atomic nuclei that have collided with cosmic rays. Within the cores of stars beryllium is depleted as it is fused and creates larger elements. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl (aquamarine, emerald) and chrysoberyl. As a free element it is a steel-gray, strong, lightweight and brittle alkaline earth metal. Beryllium improves"
"model, and since the precise measurements of the cosmic microwave background by the Cosmic Background Explorer in the early 1990s, few cosmologists have seriously proposed other theories of the origin and evolution of the cosmos. One consequence of this is that in standard general relativity, the universe began with a singularity, as demonstrated by Roger Penrose and Stephen Hawking in the 1960s. An alternative view to extend the Big Bang model, suggesting the universe had no beginning or singularity and the age of the universe is infinite, has been presented. The lightest chemical elements, primarily hydrogen and helium, were created"